feat: mount Angular SPA under /ng/ prefix with root redirect}
- Bump version to v2026.4.322 - Move Angular static serving from / to /ng/ path prefix - Add root / route that redirects to /ng/ or /react/ based on localStorage preference (p3xr-frontend key) - Simplify Angular SPA fallback to only handle /ng/* routes, removing unnecessary /socket.io and /react path checks - Update version references in README.md and artifacts/cluster.md