feat: add meta hints user marks for metadata heuristic override

Users can now right-click nodes and assign meta hints
(primary_model, primary_sampler, positive_prompt,
negative_prompt) to override the metadata processor's
heuristic inference.

- Store extra_data from the API request so workflow node
  properties (including lm_marker_role) are accessible
  during metadata processing.
- _get_user_marks scans extra_data.extra_pnginfo.workflow
  for meta_* marks, falling back to prompt.original_prompt.
- extract_generation_params checks user marks before
  heuristic inference for sampler, model, and prompts.
- Warn on duplicate marks or invalid marked nodes.

py/metadata_collector/metadata_registry.py

@@ -61,6 +61,7 @@ class MetadataRegistry:
             {
                 "execution_order": [],
                 "current_prompt": None,  # Will store the prompt object
+                "extra_data": None,  # Will store the API extra_data for workflow metadata
                 "timestamp": time.time(),
             }
         )
@@ -75,6 +76,11 @@ class MetadataRegistry:
             # Store the prompt in the metadata for later relationship tracing
             self.prompt_metadata[self.current_prompt_id]["current_prompt"] = prompt
 
+    def set_extra_data(self, extra_data):
+        """Store the API extra_data (contains extra_pnginfo.workflow with node properties)"""
+        if self.current_prompt_id and self.current_prompt_id in self.prompt_metadata:
+            self.prompt_metadata[self.current_prompt_id]["extra_data"] = extra_data
+
     def get_metadata(self, prompt_id=None):
         """Get collected metadata for a prompt"""
         key = prompt_id if prompt_id is not None else self.current_prompt_id