Fix 8 bugs from second code review

HIGH:
- Fix JS TypeError on empty API response: validate keys/types are arrays
  before using them; add HTTP status check (resp.ok)
- Fix BEGIN IMMEDIATE conflict: set isolation_level=None (autocommit) on
  SQLite connection so explicit transactions work without implicit ones

MEDIUM:
- Fix import_json_file non-atomic: wrap entire operation in BEGIN/COMMIT
  with ROLLBACK on error — no more partial imports
- Fix crash on non-dict batch_data items: skip non-dict elements
- Fix comma-in-key corruption: store keys/types as JSON arrays in hidden
  widgets instead of comma-delimited strings (backward-compat fallback)
- Fix blocking I/O in API routes: change async def to def so FastAPI
  auto-threads the synchronous SQLite calls

LOW:
- Fix missing ?. on app.graph.setDirtyCanvas in refreshDynamicOutputs

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

utils.py

@@ -221,9 +221,9 @@ def sync_to_db(db, project_name: str, file_path: Path, data: dict) -> None:
                     (df_id, json.dumps(history_tree), now),
                 )
 
-            db.conn.commit()
+            db.conn.execute("COMMIT")
         except Exception:
-            db.conn.rollback()
+            db.conn.execute("ROLLBACK")
             raise
     except Exception as e:
         logger.warning(f"sync_to_db failed: {e}")