feat(02-01): create bot main.py with Application setup

- ApplicationBuilder with post_init/post_shutdown hooks
- Database lifecycle (init_db, create_tables, close_db)
- Config stored in bot_data for handler access
- Calls register_handlers before run_polling

src/moai/bot/main.py

@@ -0,0 +1,82 @@
+"""MoAI Telegram bot entry point.
+
+Sets up and runs the Telegram bot with database lifecycle hooks.
+
+Usage:
+    python -m moai.bot.main
+"""
+
+import logging
+
+from telegram.ext import Application, ApplicationBuilder
+
+from moai.bot.config import BotConfig
+from moai.bot.handlers import register_handlers
+from moai.core.database import close_db, create_tables, init_db
+
+# Module-level config reference for post_init callback
+_config: BotConfig | None = None
+
+
+async def post_init(application: Application) -> None:
+    """Initialize database after bot application is built.
+
+    Called automatically by python-telegram-bot after Application.build().
+    Sets up the database engine and creates tables if needed.
+    """
+    logger = logging.getLogger(__name__)
+
+    if _config is None:
+        raise RuntimeError("Config not initialized before post_init")
+
+    init_db(_config.database_url)
+    await create_tables()
+    logger.info("Database initialized")
+
+
+async def post_shutdown(application: Application) -> None:
+    """Clean up database on bot shutdown.
+
+    Called automatically by python-telegram-bot during Application shutdown.
+    Disposes database engine and releases connections.
+    """
+    logger = logging.getLogger(__name__)
+    await close_db()
+    logger.info("Database closed")
+
+
+def main() -> None:
+    """Run the MoAI Telegram bot.
+
+    Loads configuration from environment, sets up the Application with
+    database lifecycle hooks, registers handlers, and starts polling.
+    """
+    global _config
+
+    _config = BotConfig.from_env()
+
+    logging.basicConfig(
+        level=getattr(logging, _config.log_level.upper(), logging.INFO),
+        format="%(asctime)s - %(name)s - %(levelname)s - %(message)s",
+    )
+    logger = logging.getLogger(__name__)
+
+    app = (
+        ApplicationBuilder()
+        .token(_config.bot_token)
+        .post_init(post_init)
+        .post_shutdown(post_shutdown)
+        .build()
+    )
+
+    # Store config in bot_data for handler access
+    app.bot_data["config"] = _config
+
+    register_handlers(app)
+
+    logger.info("Starting MoAI bot...")
+    app.run_polling()
+
+
+if __name__ == "__main__":
+    main()