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- Revise technical documentation to mark Phase 5 as completed and remove outdated TODO items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.

py/services/model_scanner.py

@@ -275,16 +275,10 @@ class ModelScanner:
         _, license_flags = resolve_license_info(license_source or {})
         entry['license_flags'] = license_flags
 
-        # Handle sub_type (new canonical field) and model_type (backward compatibility)
+        # Handle sub_type (new canonical field)
         sub_type = get_value('sub_type', None)
-        model_type = get_value('model_type', None)
-        
-        # Prefer sub_type, fallback to model_type for backward compatibility
-        effective_sub_type = sub_type or model_type
-        if effective_sub_type:
-            entry['sub_type'] = effective_sub_type
-            # Also keep model_type for backward compatibility during transition
-            entry['model_type'] = effective_sub_type
+        if sub_type:
+            entry['sub_type'] = sub_type
 
         return entry