fix(tests): declare le tag OpenAPI 'Coffres Secrets' (test_used_tags_are_declared)

backend/openapi_docs.py

@@ -41,6 +41,7 @@ TAGS_METADATA: list[dict[str, str]] = [
     {"name": "Webhooks", "description": "HTTP callbacks signed with HMAC-SHA256 for file events."},
     {"name": "Conflicts", "description": "Detect and resolve Syncthing sync-conflict files."},
     {"name": "Admin", "description": "Admin-only system monitoring: stats, audit log, backup stats and live stream."},
+    {"name": "Coffres Secrets", "description": "Secret vaults: encrypted coffres, secrets, consumers, grants and distribution — metadata only, values are never exposed."},
     {"name": "Plugins", "description": "Install, enable and manage user plugins."},
     {"name": "Push", "description": "Web Push (VAPID) subscription management and test notifications."},
     {"name": "Duplicates", "description": "Duplicate-note detection and confirmed merge (#166)."},