fix: stabilize background operations and large embedding results

backend/app/log_routes.py

@@ -0,0 +1,11 @@
+from fastapi import APIRouter, Query
+from app.operation_logs import get_store
+
+router = APIRouter(prefix='/api/logs', tags=['Diagnostics'])
+
+
+@router.get('')
+def list_logs(limit: int = Query(50, ge=1, le=200), before: int | None = Query(None, ge=1),
+              level: str = Query('', pattern='^(|INFO|WARNING|ERROR|CRITICAL)$'),
+              source: str = Query('', max_length=100), q: str = Query('', max_length=200)):
+    return get_store().query(limit=limit, before=before, level=level, source=source, q=q)