feat(customer): show NetBird API token renewal/expiry date

Displays when the per-customer token was last (re-)issued and its
computed expiry (365 days from renewal) on the Auto-Updates card, so it's
visible at a glance without checking the database.

static/lang/en.json

@@ -98,6 +98,8 @@
     "nbuSaveToken": "Verify & Save",
     "nbuTokenSaved": "Token saved.",
     "nbuChangeToken": "Change token",
+    "nbuTokenRenewed": "Token renewed on {date}",
+    "nbuTokenExpires": "valid until {date}",
     "nbuVersion": "Client version",
     "nbuDisabled": "Disabled",
     "nbuLatest": "Latest version",