feat(web): branded green PWA icons + maskable, installable app polish

Replace the stale blue calendar icon with the real green Calendarr app
icon (matching iOS/Android) for the installable web app:
- icon-192/512.png regenerated from the branded 1024 app icon
- add dedicated maskable icons (192/512) with brand-green safe-zone
  padding so Android/Chrome render a proper adaptive icon (no white box)
- manifest: maskable purpose entries, id, description, lang/dir,
  categories; theme_color -> brand green (#16713d)
- index.html: theme-color -> green, add modern mobile-web-app-capable
- favicon.svg + icon.svg recolored to brand green
Bump APP_VERSION v89 -> v90.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/favicon.svg

@@ -1,4 +1,4 @@
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="#4285f4" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="#2ea05a" stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
   <rect x="3" y="4" width="18" height="18" rx="2"/>
   <line x1="16" y1="2" x2="16" y2="6"/>
   <line x1="8" y1="2" x2="8" y2="6"/>