gate: wrap db.commit() in try/except after plugin activation

app/main.py

@@ -241,7 +241,11 @@ async def lifespan(app: FastAPI):
             plugin_record.status = "active"
             logger.info(f"[STARTUP] Activated plugin: {name}")
 
-        await db.commit()
+        try:
+            await db.commit()
+        except Exception as exc:
+            logger.warning(f"[STARTUP] Commit failed after plugin activation: {exc}")
+            await db.rollback()
 
     # Initialize permission registry with active plugin names
     from app.core.permission_registry import init_permission_registry, register_plugin_permissions