feat: mobile UI overhaul — iPhone-style app grid, icon-only tab bar, fullscreen app sessions

- Add AppIconGrid: 4-column swipeable icon grid with page dots for My Apps on mobile
- Tab bar: remove text labels, square icon-only buttons (w-14 h-14), doubled padding
- Hide tab bar and top context tabs when app session is open
- App session header hidden on mobile, replaced with floating glass close button
- App sessions now render fullscreen on mobile without nav chrome

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

neode-ui/src/views/appSession/AppSessionHeader.vue

@@ -1,5 +1,5 @@
 <template>
-  <div class="sticky top-0 z-10 flex items-center gap-3 border-b border-white/10 px-4 py-3 bg-black/60 backdrop-blur-md md:bg-transparent md:backdrop-blur-none">
+  <div class="sticky top-0 z-10 hidden md:flex items-center gap-3 border-b border-white/10 px-4 py-3 bg-black/60 backdrop-blur-md md:bg-transparent md:backdrop-blur-none">
     <!-- Back / Forward navigation -->
     <div class="flex items-center gap-0.5">
       <button class="app-session-btn" aria-label="Back" title="Go back" @click="$emit('goBack')">