Root-level PWA files (manifest.webmanifest, sw.js, registerSW.js, workbox-*.js,
icon-*.png, apple-touch-icon.png) were falling through to the index.html
catch-all and returning HTML — breaking the manifest (syntax error) and
preventing the service worker from ever registering. serveStatic('/*') serves
any existing file and calls next() for SPA routes, so index.html stays the
fallback. Registered after /health, /api/*, /callback so those still win.