Port dynamic node improvements from ComfyUI-JSON-Dynamic

- Deferred output cleanup (_configured flag + queueMicrotask) to prevent
  breaking links when other nodes (e.g. Kijai Set/Get) resolve outputs
  during graph loading
- file_not_found error handling in refresh to keep existing outputs intact
- Fallback widget sync in onConfigure when widget values are empty but
  serialized outputs exist

Applied to both json_dynamic.js and project_dynamic.js.

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

json_loader.py

@@ -75,6 +75,8 @@ if PromptServer is not None:
         except (ValueError, TypeError):
             seq = 1
         data = read_json_data(json_path)
+        if not data:
+            return web.json_response({"keys": [], "types": [], "error": "file_not_found"})
         target = get_batch_item(data, seq)
         keys = []
         types = []