refactor(model-type): complete phase 5 cleanup by removing deprecated model_type field

- Remove backward compatibility code for `model_type` in `ModelScanner._build_cache_entry()`
- Update `CheckpointScanner` to only handle `sub_type` in `adjust_metadata()` and `adjust_cached_entry()`
- Delete deprecated aliases `resolve_civitai_model_type` and `normalize_civitai_model_type` from `model_query.py`
- Update frontend components (`RecipeModal.js`, `ModelCard.js`, etc.) to use `sub_type` instead of `model_type`
- Update API response format to return only `sub_type`, removing `model_type` from service responses
- Revise technical documentation to mark Phase 5 as completed and remove outdated TODO items

All cleanup tasks for the model type refactoring are now complete, ensuring consistent use of `sub_type` across the codebase.

tests/services/test_checkpoint_scanner.py

@@ -126,7 +126,7 @@ async def test_persisted_cache_restores_model_type(tmp_path: Path, monkeypatch):
     assert loaded is True
 
     cache = await scanner.get_cached_data()
-    types_by_path = {item["file_path"]: item.get("model_type") for item in cache.raw_data}
+    types_by_path = {item["file_path"]: item.get("sub_type") for item in cache.raw_data}
 
     assert types_by_path[normalized_checkpoint_file] == "checkpoint"
     assert types_by_path[normalized_unet_file] == "diffusion_model"