feat: add photography wallpaper gallery

[enescala]

Summary

• add a four-column photography browser to Background settings
• load more photos as the gallery approaches the bottom, with bounded duplicate retries, error recovery, and a per-category cache
• apply a selected photo immediately and keep its Unsplash attribution metadata
• prevent in-flight refreshes from overwriting manual selections or newer category requests
• make the settings panel scroll cleanly on smaller viewports
• configure Netlify previews to use the current Vite build and a supported Node runtime

The current GraphQL API exposes one random photo per request, so gallery pages are assembled from small concurrent request batches and deduplicated client-side.

Screenshots

Browse photography

Select a background

Testing

• ./node_modules/.bin/vite build
• exercised the gallery in headless Chromium and confirmed scrolling increased the rendered photos from 12 to 16
• selected a thumbnail and confirmed both the background and selected state updated
• Netlify deploy preview