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/main.py

@@ -189,7 +189,8 @@ async def start_download(body: DownloadIn) -> dict:
 @app.get("/api/civitai/search")
 async def civitai_search(
     query: Optional[str] = None,
-    types: Optional[str] = None,   # comma-separated CivitAI types
+    types: Optional[str] = None,        # comma-separated CivitAI types
+    base_models: Optional[str] = None,  # comma-separated CivitAI base models
     sort: Optional[str] = "Most Downloaded",
     period: Optional[str] = "AllTime",
     nsfw: bool = False,
@@ -199,10 +200,11 @@ async def civitai_search(
     if not db.get_setting("civitai_api_key"):
         raise HTTPException(400, "Set your CivitAI API key in Settings first.")
     type_list = [t for t in (types or "").split(",") if t] or None
+    base_model_list = [b for b in (base_models or "").split(",") if b] or None
     try:
         return await registries.civitai_search(
-            query=query, types=type_list, sort=sort, period=period,
-            nsfw=nsfw, page=page, cursor=cursor)
+            query=query, types=type_list, base_models=base_model_list,
+            sort=sort, period=period, nsfw=nsfw, page=page, cursor=cursor)
     except Exception as exc:  # noqa: BLE001 - surface API errors to the UI
         raise HTTPException(502, f"CivitAI search failed: {exc}")