fix(caddy): route relay WebSocket traffic to relay container

Add /relay* location block to Caddyfile template so that NetBird relay
WebSocket connections (rels://) are correctly forwarded to the relay
container instead of falling through to the dashboard handler.

Without this fix, all relay WebSocket connections silently hit the
dashboard container, causing STUN/relay connectivity failures for all
deployed NetBird instances.

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

app/services/npm_service.py

@@ -259,7 +259,16 @@ async def create_proxy_host(
         "block_exploits": True,
         "allow_websocket_upgrade": True,
         "access_list_id": 0,
-        "advanced_config": "",
+        "advanced_config": (
+            "location ^~ /management.ManagementService/ {\n"
+            f"    grpc_pass grpc://{forward_host}:{forward_port};\n"
+            "    grpc_set_header Host $host;\n"
+            "}\n"
+            "location ^~ /signalexchange.SignalExchange/ {\n"
+            f"    grpc_pass grpc://{forward_host}:{forward_port};\n"
+            "    grpc_set_header Host $host;\n"
+            "}\n"
+        ),
         "meta": {
             "letsencrypt_agree": True,
             "letsencrypt_email": admin_email,

templates/Caddyfile.j2

@@ -29,6 +29,11 @@
 		}
 	}
 
+	# NetBird Relay WebSocket (rels://)
+	handle /relay* {
+		reverse_proxy netbird-{{ subdomain }}-relay:80
+	}
+
 	# Default: NetBird Dashboard
 	handle {
 		reverse_proxy netbird-{{ subdomain }}-dashboard:80