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/views/OnboardingOptions.vue

@@ -4,7 +4,7 @@
       <div class="text-center mb-8">
         <div class="logo-gradient-border inline-block mb-8">
           <img 
-            src="/assets/img/favico.svg" 
+            src="/assets/icon/favico-black-v2.svg" 
             alt="Archipelago" 
             class="w-20 h-20"
           />