Web: redesign, logo, PWA, QR codes, Spotify guidance

- Album-art-tinted cards that crossfade on song change, equalizer bars,
  live avatar rings, drifting ambient colour, Space Grotesk display font,
  brand purple-to-blue gradient from the logo
- Feed cards rise in and glide to new positions (motion); respects
  reduced-motion
- New logo as nav mark, favicon and Apple touch icon
- Installable PWA: manifest, maskable icons, small service worker
  (cached build assets + offline page), security headers
- Show-QR-code on your own profile; centred profile header with stats
- Settings explains connecting Spotify via Last.fm or ListenBrainz

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/web/src/app/manifest.ts

@@ -0,0 +1,22 @@
+import type { MetadataRoute } from 'next';
+
+/** Makes the website installable ("Add to Home Screen") as a standalone app. Needs HTTPS in production. */
+export default function manifest(): MetadataRoute.Manifest {
+  return {
+    name: 'musicshare',
+    short_name: 'musicshare',
+    description: 'See what your friends are listening to, and play it on your own service.',
+    start_url: '/',
+    scope: '/',
+    display: 'standalone',
+    orientation: 'portrait',
+    background_color: '#07070b',
+    theme_color: '#07070b',
+    categories: ['music', 'social'],
+    icons: [
+      { src: '/icon-192.png', sizes: '192x192', type: 'image/png', purpose: 'any' },
+      { src: '/icon-512.png', sizes: '512x512', type: 'image/png', purpose: 'any' },
+      { src: '/icon-maskable-512.png', sizes: '512x512', type: 'image/png', purpose: 'maskable' },
+    ],
+  };
+}