feat(config): enable DCR for multi-user BasicAuth with offline access

Allows multi-user BasicAuth mode to use Dynamic Client Registration (DCR)
for OAuth credentials when ENABLE_OFFLINE_ACCESS is enabled, making it
consistent with OAuth modes and reducing configuration burden.

**Changes:**

Configuration Validation:
- Relaxed OAuth credential requirements for multi-user BasicAuth
- OAuth credentials now optional when offline access enabled
- Will use DCR as fallback if NEXTCLOUD_OIDC_CLIENT_ID/SECRET not set
- Updated validation to log info instead of error when DCR will be used

Startup Logic (app.py):
- Added DCR workflow for multi-user BasicAuth before uvicorn starts
- Creates oauth_context for management APIs when offline access enabled
- Allows Astrolabe to authenticate management API calls with OAuth
- DCR runs synchronously at same lifecycle point as OAuth modes
- Added traceback import for better error logging
- Fixed type assertions for nextcloud_host
- Fixed undefined variable references in vector sync logging

Management API:
- Improved auth mode detection using proper detect_auth_mode()
- Added auth_mode field to /status endpoint:
  * "basic" - Single-user BasicAuth
  * "multi_user_basic" - Multi-user BasicAuth
  * "oauth" - OAuth modes
  * "smithery" - Smithery stateless
- Added supports_app_passwords indicator for multi-user BasicAuth

Docker Compose:
- Updated mcp-multi-user-basic service configuration:
  * Enabled vector sync (VECTOR_SYNC_ENABLED=true)
  * Added ENABLE_OFFLINE_ACCESS=true for app password support
  * Added NEXTCLOUD_MCP_SERVER_URL for Astrolabe integration
  * Documented optional static OAuth credentials

Testing:
- Updated test_config_validators.py to expect DCR fallback
- Enhanced configure_astrolabe_for_mcp_server fixture with verification
- Added debug logging to test_users_setup fixture

**Workflow:**
1. User configures ENABLE_OFFLINE_ACCESS=true
2. Server checks for static NEXTCLOUD_OIDC_CLIENT_ID/SECRET
3. If not found, performs DCR before uvicorn starts
4. DCR registers client with Nextcloud OIDC provider
5. OAuth credentials used for Astrolabe management API auth
6. Background sync can retrieve user app passwords via Astrolabe

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

nextcloud_mcp_server/api/management.py

@@ -182,14 +182,23 @@ async def get_server_status(request: Request) -> JSONResponse:
     # Calculate uptime
     uptime_seconds = int(time.time() - _server_start_time)
 
-    # Determine auth mode
-    nextcloud_username = os.getenv("NEXTCLOUD_USERNAME")
-    nextcloud_password = os.getenv("NEXTCLOUD_PASSWORD")
+    # Determine auth mode using proper mode detection
+    from nextcloud_mcp_server.config_validators import AuthMode, detect_auth_mode
 
-    if nextcloud_username and nextcloud_password:
-        auth_mode = "basic"
-    else:
+    mode = detect_auth_mode(settings)
+
+    # Map deployment mode to auth_mode for API response
+    # This helps clients (like Astrolabe) determine which auth flow to use
+    if mode == AuthMode.OAUTH_SINGLE_AUDIENCE or mode == AuthMode.OAUTH_TOKEN_EXCHANGE:
         auth_mode = "oauth"
+    elif mode == AuthMode.MULTI_USER_BASIC:
+        auth_mode = "multi_user_basic"
+    elif mode == AuthMode.SINGLE_USER_BASIC:
+        auth_mode = "basic"
+    elif mode == AuthMode.SMITHERY_STATELESS:
+        auth_mode = "smithery"
+    else:
+        auth_mode = "unknown"
 
     response_data = {
         "version": __version__,
@@ -199,6 +208,10 @@ async def get_server_status(request: Request) -> JSONResponse:
         "management_api_version": "1.0",
     }
 
+    # Add app password support indicator for multi-user BasicAuth mode
+    if mode == AuthMode.MULTI_USER_BASIC:
+        response_data["supports_app_passwords"] = settings.enable_offline_access
+
     # Include OIDC configuration if in OAuth mode
     if auth_mode == "oauth":
         # Provide IdP discovery information for NC PHP app