chore: update entry points for multi-account

- main.py calls migrate_legacy_state() before starting server
- health.py accepts account_ids parameter for per-account health checks
- _continuous_check returns per-account status instead of single snapshot

main.py

@@ -1,5 +1,6 @@
 import logging
 import sys
+from pathlib import Path
 
 from webui_server import run_server
 
@@ -11,6 +12,20 @@ def main():
         datefmt="%Y-%m-%d %H:%M:%S",
         stream=sys.stdout,
     )
+
+    logger = logging.getLogger(__name__)
+
+    # Run legacy migration before starting the server
+    from app_state import migrate_legacy_state
+
+    data_dir = Path("data")
+    session_dir = Path("session")
+    try:
+        if migrate_legacy_state(data_dir, session_dir):
+            logger.info("Legacy migration completed successfully.")
+    except Exception as exc:
+        logger.error("Migration failed: %s", exc)
+
     run_server()