feat(updates): NetBird container image update management

- New image_service.py: Docker Hub digest check (no pull), local digest/ID
  comparison, pull_all_images, per-customer container image status, and
  update_customer_containers (docker compose up -d, data-safe)
- Monitoring endpoints: GET /images/check (hub vs local + per-customer
  needs_update), POST /images/pull (background), POST /customers/update-all
- Deployment endpoint: POST /{id}/update-images (single-customer update)
- Monitoring page: "NetBird Container Updates" card with Check / Pull / Update
  All buttons; image status table and per-customer update table with inline
  update buttons
- i18n: added keys in en.json and de.json

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

static/index.html

@@ -1152,7 +1152,7 @@
                 </div>
 
                 <!-- Customer Statuses -->
-                <div class="card shadow-sm">
+                <div class="card shadow-sm mb-4">
                     <div class="card-header" data-i18n="monitoring.allCustomerDeployments">All Customer Deployments
                     </div>
                     <div class="table-responsive">
@@ -1178,6 +1178,27 @@
                         </table>
                     </div>
                 </div>
+
+                <!-- NetBird Container Updates -->
+                <div class="card shadow-sm">
+                    <div class="card-header d-flex justify-content-between align-items-center">
+                        <span><i class="bi bi-arrow-repeat me-2"></i><span data-i18n="monitoring.imageUpdates">NetBird Container Updates</span></span>
+                        <div class="d-flex gap-2">
+                            <button class="btn btn-outline-secondary btn-sm" onclick="checkImageUpdates()" id="btn-check-updates">
+                                <i class="bi bi-search me-1"></i><span data-i18n="monitoring.checkUpdates">Check for Updates</span>
+                            </button>
+                            <button class="btn btn-outline-primary btn-sm" onclick="pullAllImages()" id="btn-pull-images">
+                                <i class="bi bi-cloud-download me-1"></i><span data-i18n="monitoring.pullImages">Pull Latest Images</span>
+                            </button>
+                            <button class="btn btn-warning btn-sm d-none" onclick="updateAllCustomers()" id="btn-update-all">
+                                <i class="bi bi-lightning-charge-fill me-1"></i><span data-i18n="monitoring.updateAll">Update All</span>
+                            </button>
+                        </div>
+                    </div>
+                    <div class="card-body" id="image-updates-body">
+                        <p class="text-muted mb-0" data-i18n="monitoring.clickCheckUpdates">Click "Check for Updates" to compare local images with Docker Hub.</p>
+                    </div>
+                </div>
             </div>
         </div>
     </div>

static/js/app.js

@@ -1633,6 +1633,144 @@ async function loadAllCustomerStatuses() {
     }
 }
 
+// ---------------------------------------------------------------------------
+// Image Updates
+// ---------------------------------------------------------------------------
+async function checkImageUpdates() {
+    const btn = document.getElementById('btn-check-updates');
+    const body = document.getElementById('image-updates-body');
+    btn.disabled = true;
+    body.innerHTML = `<div class="text-muted"><span class="spinner-border spinner-border-sm me-2"></span>${t('common.loading')}</div>`;
+
+    try {
+        const data = await api('GET', '/monitoring/images/check');
+
+        // Image status table
+        const imageRows = Object.values(data.images).map(img => {
+            const badge = img.update_available
+                ? `<span class="badge bg-warning text-dark">${t('monitoring.updateAvailable')}</span>`
+                : `<span class="badge bg-success">${t('monitoring.upToDate')}</span>`;
+            const shortDigest = d => d ? d.substring(7, 19) + '…' : '-';
+            return `<tr>
+                <td><code class="small">${esc(img.image)}</code></td>
+                <td class="small text-muted">${shortDigest(img.local_digest)}</td>
+                <td class="small text-muted">${shortDigest(img.hub_digest)}</td>
+                <td>${badge}</td>
+            </tr>`;
+        }).join('');
+
+        // Customer status table
+        const customerRows = data.customer_status.length === 0
+            ? `<tr><td colspan="3" class="text-center text-muted py-3">${t('monitoring.noCustomers')}</td></tr>`
+            : data.customer_status.map(c => {
+                const badge = c.needs_update
+                    ? `<span class="badge bg-warning text-dark">${t('monitoring.needsUpdate')}</span>`
+                    : `<span class="badge bg-success">${t('monitoring.upToDate')}</span>`;
+                const updateBtn = c.needs_update
+                    ? `<button class="btn btn-sm btn-outline-warning ms-2" onclick="updateCustomerImages(${c.customer_id})"
+                        title="${t('monitoring.updateCustomer')}"><i class="bi bi-arrow-repeat"></i></button>`
+                    : '';
+                return `<tr>
+                    <td>${c.customer_id}</td>
+                    <td>${esc(c.customer_name)} <code class="small text-muted">${esc(c.subdomain)}</code></td>
+                    <td>${badge}${updateBtn}</td>
+                </tr>`;
+            }).join('');
+
+        // Show "Update All" button if any customer needs update
+        const updateAllBtn = document.getElementById('btn-update-all');
+        if (data.customer_status.some(c => c.needs_update)) {
+            updateAllBtn.classList.remove('d-none');
+        } else {
+            updateAllBtn.classList.add('d-none');
+        }
+
+        body.innerHTML = `
+            <h6 class="mb-2">${t('monitoring.imageStatusTitle')}</h6>
+            <div class="table-responsive mb-4">
+                <table class="table table-sm mb-0">
+                    <thead class="table-light">
+                        <tr>
+                            <th>${t('monitoring.thImage')}</th>
+                            <th>${t('monitoring.thLocalDigest')}</th>
+                            <th>${t('monitoring.thHubDigest')}</th>
+                            <th>${t('monitoring.thStatus')}</th>
+                        </tr>
+                    </thead>
+                    <tbody>${imageRows}</tbody>
+                </table>
+            </div>
+            <h6 class="mb-2">${t('monitoring.customerImageTitle')}</h6>
+            <div class="table-responsive">
+                <table class="table table-sm mb-0">
+                    <thead class="table-light">
+                        <tr>
+                            <th>${t('monitoring.thId')}</th>
+                            <th>${t('monitoring.thName')}</th>
+                            <th>${t('monitoring.thStatus')}</th>
+                        </tr>
+                    </thead>
+                    <tbody>${customerRows}</tbody>
+                </table>
+            </div>`;
+    } catch (err) {
+        body.innerHTML = `<div class="alert alert-danger">${err.message}</div>`;
+    } finally {
+        btn.disabled = false;
+    }
+}
+
+async function pullAllImages() {
+    if (!confirm(t('monitoring.confirmPull'))) return;
+    const btn = document.getElementById('btn-pull-images');
+    btn.disabled = true;
+    try {
+        await api('POST', '/monitoring/images/pull');
+        showToast(t('monitoring.pullStarted'));
+        // Re-check after a few seconds to let pull finish
+        setTimeout(() => checkImageUpdates(), 5000);
+    } catch (err) {
+        showMonitoringAlert('danger', err.message);
+    } finally {
+        btn.disabled = false;
+    }
+}
+
+async function updateCustomerImages(customerId) {
+    try {
+        await api('POST', `/customers/${customerId}/update-images`);
+        showToast(t('monitoring.updateDone'));
+        setTimeout(() => checkImageUpdates(), 2000);
+    } catch (err) {
+        showMonitoringAlert('danger', err.message);
+    }
+}
+
+async function updateAllCustomers() {
+    if (!confirm(t('monitoring.confirmUpdateAll'))) return;
+    const btn = document.getElementById('btn-update-all');
+    btn.disabled = true;
+    try {
+        const data = await api('POST', '/monitoring/customers/update-all');
+        showToast(data.message || t('monitoring.updateAllStarted'));
+        setTimeout(() => checkImageUpdates(), 5000);
+    } catch (err) {
+        showMonitoringAlert('danger', err.message);
+    } finally {
+        btn.disabled = false;
+    }
+}
+
+function showMonitoringAlert(type, msg) {
+    const body = document.getElementById('image-updates-body');
+    const existing = body.querySelector('.alert');
+    if (existing) existing.remove();
+    const div = document.createElement('div');
+    div.className = `alert alert-${type} mt-2`;
+    div.textContent = msg;
+    body.prepend(div);
+}
+
 // ---------------------------------------------------------------------------
 // Helpers
 // ---------------------------------------------------------------------------

static/lang/de.json

@@ -373,6 +373,25 @@
     "thDashboard": "Dashboard",
     "thRelayPort": "Relay-Port",
     "thContainers": "Container",
-    "noCustomers": "Keine Kunden."
+    "noCustomers": "Keine Kunden.",
+    "imageUpdates": "NetBird Container Updates",
+    "checkUpdates": "Auf Updates prüfen",
+    "pullImages": "Neueste Images laden",
+    "updateAll": "Alle aktualisieren",
+    "clickCheckUpdates": "Klicken Sie auf \"Auf Updates prüfen\" um lokale Images mit Docker Hub zu vergleichen.",
+    "updateAvailable": "Update verfügbar",
+    "upToDate": "Aktuell",
+    "needsUpdate": "Update erforderlich",
+    "updateCustomer": "Diesen Kunden aktualisieren",
+    "imageStatusTitle": "Image-Status (vs. Docker Hub)",
+    "customerImageTitle": "Kunden-Container Status",
+    "thImage": "Image",
+    "thLocalDigest": "Lokaler Digest",
+    "thHubDigest": "Hub Digest",
+    "confirmPull": "Neueste NetBird Images von Docker Hub laden? Dies kann einige Minuten dauern.",
+    "pullStarted": "Image-Download im Hintergrund gestartet. Prüfung in 5 Sekunden…",
+    "confirmUpdateAll": "Container aller Kunden mit veralteten Images neu erstellen? Laufende Dienste werden kurz neu gestartet.",
+    "updateAllStarted": "Aktualisierung im Hintergrund gestartet.",
+    "updateDone": "Kunden-Container aktualisiert."
   }
 }

static/lang/en.json

@@ -280,7 +280,26 @@
     "thDashboard": "Dashboard",
     "thRelayPort": "Relay Port",
     "thContainers": "Containers",
-    "noCustomers": "No customers."
+    "noCustomers": "No customers.",
+    "imageUpdates": "NetBird Container Updates",
+    "checkUpdates": "Check for Updates",
+    "pullImages": "Pull Latest Images",
+    "updateAll": "Update All",
+    "clickCheckUpdates": "Click \"Check for Updates\" to compare local images with Docker Hub.",
+    "updateAvailable": "Update available",
+    "upToDate": "Up to date",
+    "needsUpdate": "Needs update",
+    "updateCustomer": "Update this customer",
+    "imageStatusTitle": "Image Status (vs. Docker Hub)",
+    "customerImageTitle": "Customer Container Status",
+    "thImage": "Image",
+    "thLocalDigest": "Local Digest",
+    "thHubDigest": "Hub Digest",
+    "confirmPull": "Pull the latest NetBird images from Docker Hub? This may take a few minutes.",
+    "pullStarted": "Image pull started in background. Re-checking in 5 seconds…",
+    "confirmUpdateAll": "Recreate containers for all customers that have outdated images? Running services will briefly restart.",
+    "updateAllStarted": "Update started in background.",
+    "updateDone": "Customer containers updated."
   },
   "userModal": {
     "title": "New User",