Port frontend from Astro to Vite + React Router SPA

[devin-ai-integration]

Summary

This PR migrates the frontend from Astro to a Vite + React Router single-page application (SPA). This change is required because Discord Activities require SPAs for proper functionality.

Key changes:

• Replace Astro build tooling with Vite
• Add React Router for client-side routing instead of Astro's file-based routing
• Convert Astro pages (.astro files) to React page components
• Remove Astro-specific components (MiniRouter, RoomLoaderAutomatic, AdminRoomEditPage) and replace with React Router equivalents
• Update backend to serve Vite's build output (/assets instead of /_astro) and serve index.html for all frontend routes (SPA fallback)

Updates since last revision

• Fixed assets routing bug: removed app.all("/assets/:unused", proxyDownstream) which was incorrectly proxying frontend assets to Broadcast Box instead of serving them from the static folder
• Fixed Dockerfile: changed npm ci --only=production to npm ci for frontend so vite (a devDependency) is available during build
• Added .dockerignore to exclude node_modules and dist folders, ensuring reproducible Docker builds across environments
• Replaced location.href with React Router navigation in DiscordMagicRedirect.jsx, DiscordRoomRedirector.jsx, and utils.js to ensure Discord Activities won't kill the app due to top-level navigation. The checkChannelRoomAssociation function now accepts an optional navigateFn callback parameter.

Review & Testing Checklist for Human

• Test Discord Activity integration - This is the primary reason for the migration. Verify the app works correctly when embedded as a Discord Activity (hostname ending in .discordsays.com). Specifically verify that navigating between routes does NOT cause a full page reload.
• Test Docker build in clean environment - The Dockerfile was fixed after discovering it only worked locally due to node_modules being copied in. Verify docker compose build works from a clean checkout.
• Test WebRTC room viewing - Navigate to /room/{roomId} and verify video streaming works.
• Test admin panel with basic auth - The admin routes now serve the same index.html as other routes. Verify basic auth still protects the admin API endpoints and the UI works.
• Test fullscreen mode - Add ?fullscreen=1 to a room URL and verify the fullscreen styling applies correctly.

Recommended Test Plan

1. Clone the repo fresh (or delete node_modules and dist folders)
2. Run docker compose build && docker compose up
3. Test each route: /, /room, /room/{id}, /discord, /admin, /admin/room/{id}
4. If possible, test as a Discord Activity to verify the SPA requirement is satisfied and navigation doesn't cause page reloads

Local Testing Screenshots

Notes

• Link to Devin run: https://app.devin.ai/sessions/04a005efc4f14ae6bff6537b76c7e6a8
• Requested by: Raymond / @javaarchive
• Local testing confirmed basic routes render correctly with Pico CSS styling
• WebRTC streaming was not tested due to Broadcast Box setup requirements
• The /publish/:key route still uses location.href intentionally since it proxies to Broadcast Box and won't be used in Discord Activities

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