Fix AlertRule initialization to use config_id instead of config_file

Updated init_db.py to use config_id field after database migration,
fixing container startup error on new systems.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/init_db.py

@@ -98,7 +98,7 @@ def init_default_alert_rules(session):
             'webhook_enabled': False,
             'severity': 'critical',
             'filter_conditions': None,
-            'config_file': None
+            'config_id': None
         }
     ]
 
@@ -113,7 +113,7 @@ def init_default_alert_rules(session):
                 webhook_enabled=rule_data['webhook_enabled'],
                 severity=rule_data['severity'],
                 filter_conditions=rule_data['filter_conditions'],
-                config_file=rule_data['config_file'],
+                config_id=rule_data['config_id'],
                 created_at=datetime.now(timezone.utc),
                 updated_at=datetime.now(timezone.utc)
             )