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

tests/services/test_model_scanner.py

@@ -967,6 +967,8 @@ def _make_cache_entry(**overrides) -> Dict[str, Any]:
         "source_platform": "",
         "source_url": "",
         "hf_url": "",
+        "source_model_id": "",
+        "source_version_id": "",
         "license_flags": 113,
         "hash_status": "completed",
     }
@@ -1005,6 +1007,8 @@ async def test_sync_cache_no_change(tmp_path: Path):
         "tags": ["alpha"],
         "civitai": {"id": 111, "modelId": 222, "name": "v1"},
         "hf_url": "",
+        "source_model_id": "",
+        "source_version_id": "",
     }
 
     changed = await scanner.sync_cache_from_metadata(
@@ -1049,6 +1053,8 @@ async def test_sync_cache_in_place_update(tmp_path: Path):
         "tags": ["beta", "gamma"],
         "civitai": {"id": 111, "modelId": 222, "name": "v1"},
         "hf_url": "",
+        "source_model_id": "",
+        "source_version_id": "",
     }
 
     changed = await scanner.sync_cache_from_metadata(
@@ -1094,6 +1100,8 @@ async def test_sync_cache_not_in_cache_delegates(tmp_path: Path):
         "tags": [],
         "civitai": {},
         "hf_url": "",
+        "source_model_id": "",
+        "source_version_id": "",
     }
 
     changed = await scanner.sync_cache_from_metadata(
@@ -1147,6 +1155,8 @@ async def test_sync_cache_conditional_resort_skipped(tmp_path: Path, monkeypatch
         "tags": ["alpha"],
         "civitai": {"id": 111, "modelId": 222, "name": "v1"},
         "hf_url": "",
+        "source_model_id": "",
+        "source_version_id": "",
     }
 
     changed = await scanner.sync_cache_from_metadata(
@@ -1197,6 +1207,8 @@ async def test_sync_cache_conditional_resort_triggered(tmp_path: Path, monkeypat
         "tags": ["alpha"],
         "civitai": {"id": 111, "modelId": 222, "name": "v1"},
         "hf_url": "",
+        "source_model_id": "",
+        "source_version_id": "",
     }
 
     changed = await scanner.sync_cache_from_metadata(