feat(model-manager): add CivitAI browse view + fix civitai.red / 401

- New "Browse CivitAI" view: thumbnail grid with search, type/sort/period
  filters and NSFW toggle; click a model card to download it (per-card
  version picker for multi-version models). Cursor + page based "Load more".
- Backend: /api/civitai/search and /api/civitai/download endpoints; new
  civitai_search() catalog helper.
- Fix 401 on paste: recognize the civitai.red mirror (and any civitai.*
  host), normalize API calls to civitai.com, and always resolve the
  model-version so type + filename are auto-detected for every CivitAI URL.

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

README.md

@@ -235,11 +235,14 @@ SparkyUI includes a **StabilityMatrix-style Model Manager** - a lightweight Fast
 **Access:** `http://<your-dgx-ip>:8189`
 
 **Features:**
+- **Browse CivitAI** - search the CivitAI catalog in a thumbnail grid (filter by type,
+  sort, period, NSFW toggle) and **click a model to download it** - no URL pasting needed.
+  Multi-version models get a version picker on the card.
 - **Installed Models** - browse what's on disk, grouped by type, with size and delete actions
 - **Add / Download** - paste a download URL and pick a type; live progress bars
   - **Direct URLs** - any direct download link
-  - **CivitAI** - paste a model page link (`civitai.com/models/...`) or an
-    `api/download/models/...` link; the type and filename are auto-detected
+  - **CivitAI** - paste a model page link (`civitai.com/models/...`, the `civitai.red`
+    mirror, or an `api/download/models/...` link); the type and filename are auto-detected
   - **HuggingFace** - paste a `resolve` URL (works with gated repos via your token)
 - **Settings** - store your **CivitAI API key** and **HuggingFace token** persistently
   (saved to a SQLite DB under `./sparkyui-data`, never committed to git)