Remove /ui redirect routes, add 404 page, update README

- Remove obsolete /ui, /ui/login, /ui/register, /ui/logout redirects
- Fix /ui/login links to use /login directly
- Add styled 404 page for HTML requests
- Add Web UI section to README documenting routes

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

@@ -24,7 +24,19 @@ celery -A celery_app worker --loglevel=info
 python server.py
 ```
 
-## L1 Server API
+## Web UI
+
+The server provides a web interface at the root URL:
+
+| Path | Description |
+|------|-------------|
+| `/` | Home page with server info |
+| `/runs` | View and manage rendering runs |
+| `/recipes` | Browse and run available recipes |
+| `/media` | Browse cached media files |
+| `/run/{id}` | Run detail page |
+
+## API
 
 Interactive docs: http://localhost:8100/docs