Add rotating file logging

Logs go to bot.log in the project root by default (10 MB, 3 backups).
Set LOG_FILE env var to override the path.

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

main.py

@@ -2,26 +2,46 @@ from __future__ import annotations
 
 import asyncio
 import logging
+import logging.handlers
+import os
 from pathlib import Path
 
 from app.config import load_app_config
 from app.manager import AccountManager
 
+LOG_FORMAT = "%(asctime)s | %(levelname)s | %(name)s | %(message)s"
 
-def configure_logging() -> None:
+
+def configure_logging(root: Path) -> None:
     logging.basicConfig(
         level=logging.INFO,
-        format="%(asctime)s | %(levelname)s | %(name)s | %(message)s",
+        format=LOG_FORMAT,
     )
 
+    log_file_env = os.environ.get("LOG_FILE")
+    log_path = Path(log_file_env).expanduser() if log_file_env else root / "bot.log"
+    if not log_path.is_absolute():
+        log_path = (root / log_path).resolve()
+
+    file_handler = logging.handlers.RotatingFileHandler(
+        log_path,
+        maxBytes=10 * 1024 * 1024,
+        backupCount=3,
+        encoding="utf-8",
+    )
+    file_handler.setFormatter(logging.Formatter(LOG_FORMAT))
+    logging.getLogger().addHandler(file_handler)
+
+
+_ROOT = Path(__file__).resolve().parent
+
 
 async def main() -> None:
-    root = Path(__file__).resolve().parent
-    config = load_app_config(root)
+    config = load_app_config(_ROOT)
     manager = AccountManager(config)
     await manager.run()
 
 
 if __name__ == "__main__":
-    configure_logging()
+    configure_logging(_ROOT)
     asyncio.run(main())