fix: TTLock — revert to 2-field credentials, improve UI hints

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

backend/src/routes/ttlock.ts

@@ -65,11 +65,11 @@ const ttlockRoutes: FastifyPluginAsync = async (fastify) => {
   // ── PATCH /api/hotels/:slug/ttlock/config ───────────────────────────────────
   fastify.patch<SlugParam & {
     Body: {
-      is_enabled?:     boolean
-      client_id?:      string
-      client_secret?:  string
-      card_sectors?:   string
-      api_server?:     string
+      is_enabled?:    boolean
+      client_id?:     string
+      client_secret?: string
+      card_sectors?:  string
+      api_server?:    string
     }
   }>('/api/hotels/:slug/ttlock/config', { onRequest: [fastify.authenticate] }, async (req, reply) => {
     const { slug } = req.params