feat(model-manager): generated-photo Gallery + device-routing landing

- Gallery view: grid of generated photos from ComfyUI's output/, full-size
  lightbox, and permanent delete (with confirm). Paginated ("Load more").
- Backend: GET /api/gallery, GET /gallery/file (path-guarded image serve),
  DELETE /api/gallery (path-guarded; clear error on permission denial).
- Mount ./output read-write into model-manager so the gallery can delete.
- Device-routing landing at /start: phones -> ComfyUIMini, desktops ->
  the Gallery; ?force=mobile|desktop overrides. Ports come from the new
  /api/ui-config (COMFYUI_PORT / COMFYUIMINI_PORT env).
- Responsive tweaks so the gallery is usable if opened directly on a phone.

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

README.md

@@ -235,6 +235,8 @@ SparkyUI includes a **StabilityMatrix-style Model Manager** - a lightweight Fast
 **Access:** `http://<your-dgx-ip>:8189`
 
 **Features:**
+- **Gallery** - browse generated photos from ComfyUI's `output/` in a large desktop grid,
+  click for a full-size lightbox view, and **permanently delete** photos (with confirm).
 - **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.
@@ -253,6 +255,12 @@ SparkyUI includes a **StabilityMatrix-style Model Manager** - a lightweight Fast
   by type (`checkpoints/`, `loras/`, `vae/`, `controlnet/`, `upscale_models/`, …) - these are
   created automatically on first start
 - ComfyUI mounts the same `models/` folder read-only, so new downloads appear in its loaders
+- Mounts the shared `output/` folder read-write for the Gallery's delete feature
+
+**Device-aware entry point:** open `http://<host>:8189/start` and it detects your device -
+**phones** are sent to the mobile UI (ComfyUIMini), **desktops** land on the Model Manager's
+Gallery. Append `?force=mobile` or `?force=desktop` to override. Bookmark `/start` as your
+single SparkyUI link.
 
 **Build only the Model Manager** (if the rest is already built):
 ```bash