fix: PWA improvements — clean up SW, fix chin bar, add shortcuts, improve mobile support

- Remove dead precache manifest from SW (no fetch handler to consume it)
- Set empty globPatterns in vite-plugin-pwa config
- Fix bottom chin bar padding: use scaled safe-area token instead of raw inset
- Add 'New Session' PWA shortcut (client + server manifest)
- Add PWA meta tags to mobile.html (manifest, Apple icons, theme-color)
- Fix static site.webmanifest: add id/scope, correct description
- Remove duplicate apple-mobile-web-app-title from index.html
- Move SW registration to module scope (earlier, no window.load delay)
- Update manifest route tests for new shortcut order

packages/web/public/site.webmanifest

@@ -1,8 +1,10 @@
 {
   "name": "OpenChamber",
   "short_name": "OpenChamber",
-  "description": "OpenChamber desktop companion for the OpenCode AI coding agent",
+  "description": "Web interface companion for OpenCode AI coding agent",
+  "id": "/",
   "start_url": "/",
+  "scope": "/",
   "display": "standalone",
   "background_color": "#151313",
   "theme_color": "#edb449",