fix: overhaul PWA icons with v2 suffix to bust all cache layers

- Redesign favicon SVG with gradient border matching splash screen
- Rename all icon files with -v2 suffix to bypass browser/SW/PWA caches
- Delete 9 old/duplicate icon files (~13MB removed)
- Add nginx cache-control headers for icons and manifest
- Rename assets-cache to assets-cache-v2 to orphan stale SW cache
- Update all HTML, manifest, and component icon references

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

neode-ui/src/components/PWAInstallPrompt.vue

@@ -7,7 +7,7 @@
       >
         <div class="glass-card p-4 flex items-center gap-4 shadow-xl">
           <img
-            src="/assets/icon/pwa-192x192.png"
+            src="/assets/icon/pwa-192x192-v2.png"
             alt="Archipelago"
             class="w-14 h-14 rounded-xl shrink-0"
           />