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- Revise technical documentation to mark Phase 5 as completed and remove outdated TODO items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

@@ -39,10 +39,6 @@ def normalize_sub_type(value: Any) -> Optional[str]:
     return candidate.lower() if candidate else None
 
 
-# Backward compatibility alias
-normalize_civitai_model_type = normalize_sub_type
-
-
 def resolve_sub_type(entry: Mapping[str, Any]) -> str:
     """Extract the sub-type from metadata, checking multiple sources.
     
@@ -77,10 +73,6 @@ def resolve_sub_type(entry: Mapping[str, Any]) -> str:
     return DEFAULT_CIVITAI_MODEL_TYPE
 
 
-# Backward compatibility alias
-resolve_civitai_model_type = resolve_sub_type
-
-
 class SettingsProvider(Protocol):
     """Protocol describing the SettingsManager contract used by query helpers."""