feat: multi-user isolation and graceful shutdown

- Add chat_id to events, settings, and days_off for per-user data
- Add proper graceful shutdown (signal handling, WaitGroup)
- Separate polling and webhook modes with goroutine management
- Add schema migration from single-user to multi-user schema
- Refactor handlers with shared actionFunc pattern (msg + callback)
- Fix schema path for Docker deployment (/app/db/schema.sql)
- Remove emoji from output text for cleaner formatting

docker-compose.yml

@@ -12,6 +12,7 @@ services:
       - HTTP_PROXY=${HTTP_PROXY-}
       - HTTPS_PROXY=${HTTPS_PROXY-}
       - DB_PATH=/data/db.sqlite3
+      - TZ=Asia/Tehran
     volumes:
       - worktime_data:/data