Fix image upload gallery: previews, delete, persistence

- Fix uploaded images showing as 404: /uploads/ was not excluded from the
  auth middleware matcher, so browsers were blocked from loading images.
  Added uploads to the matcher exclusion alongside images.
- Ensure uploads directory exists at startup (mkdir -p in entrypoint +
  recursive mkdir in the upload POST handler).
- Add DELETE /api/upload?url=... endpoint for admins to delete any image.
- Simplify gallery to a single unified view (no stock/uploads filter tabs).
  Each image tile shows a red × delete button on hover with confirmation.
  Upload Image button also available inside the gallery modal.
- Add Docker named volume for /app/public/uploads so uploaded images
  persist across container restarts.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -5,6 +5,8 @@ services:
     env_file: .env
     environment:
       - DATABASE_URL=postgresql://superbowl:superbowl@127.0.0.1:5432/superbowl?schema=public
+    volumes:
+      - uploads:/app/public/uploads
     depends_on:
       db:
         condition: service_healthy
@@ -25,3 +27,4 @@ services:
 
 volumes:
   pgdata:
+  uploads: