fix: stop grouping HF/ModelScope models by repository

A repository is not a model identity: collection repos on Hugging Face
and ModelScope host many unrelated models, which were wrongly shown as
versions of each other.

- Hugging Face models no longer auto-group (the Hub exposes no
  site-native model id)
- ModelScope models group by the site's native published-model id
  (MuseInfo modelVersion.modelId), extracted during enrichment and
  persisted on the sidecar as source_model_id/source_version_id;
  unenriched models stay standalone instead of collapsing a whole repo
  into one group
- TensorArt grouping unchanged (its URL id is already model-level)
- Frontend group-key derivation mirrors the new backend semantics

py/services/agent/post_processor.py

@@ -199,6 +199,15 @@ class PostProcessor:
         if is_source_model and site_version:
             self._merge_civitai(updates, metadata, name=site_version)
 
+        # Site-native identity ids (ModelScope's published model/version ids).
+        # They are what version grouping keys off, so they must reach the
+        # sidecar even when nothing else about the card changed.
+        if is_source_model and source_context is not None:
+            if source_context.source_model_id:
+                updates["source_model_id"] = source_context.source_model_id
+            if source_context.source_version_id:
+                updates["source_version_id"] = source_context.source_version_id
+
         # gallery images → civitai.images (site example images, YAML frontmatter
         # widget entries, and Sample Gallery markdown tables in the README body)
         rec_width = llm_output.get("recommended_width") or 0