feat: TTLock API server selector (EU vs China) + pass apiServer to agent

- Add api_server column to hotel_ttlock_config (migration 053)
- GET/PATCH config includes apiServer field
- issue-card passes apiServer to agent command
- Agent: WriteCardCmd.apiServer optional, all API calls use it
- TTLockPage: radio buttons EU/China with hint about 404 error

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

backend/migrations/053_ttlock_api_server.sql

@@ -0,0 +1,3 @@
+-- TTLock: выбор сервера API (EU или China)
+ALTER TABLE hotel_ttlock_config
+  ADD COLUMN IF NOT EXISTS api_server TEXT NOT NULL DEFAULT 'https://euopen.ttlock.com';