feat(model-manager): base-model multi-select filter on CivitAI browse

Add a checkbox dropdown to filter the CivitAI catalog by one or more base
models (SD 1.5, SDXL, Pony, Illustrious, Flux, etc.), mapped to the API's
`baseModels` array param. Backend search accepts comma-separated
base_models; button shows the selected count with a Clear action.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

model-manager/app/registries.py

@@ -212,6 +212,7 @@ def _to_card(item: dict) -> dict:
 
 async def civitai_search(query: Optional[str] = None,
                          types: Optional[list[str]] = None,
+                         base_models: Optional[list[str]] = None,
                          sort: Optional[str] = None,
                          period: Optional[str] = None,
                          nsfw: Optional[bool] = None,
@@ -228,6 +229,8 @@ async def civitai_search(query: Optional[str] = None,
         params["query"] = query
     if types:
         params["types"] = types  # httpx serializes lists as repeated params
+    if base_models:
+        params["baseModels"] = base_models
     if sort:
         params["sort"] = sort
     if period: