feat(app): add design system viewer, nostr feed, stop generation, and content refactor

- Design system browser with grid/detail views for tokens and components
- Nostr feed tab with note/article/zap filtering and relay status
- Stop generation button to abort AI streaming mid-response
- Paste & extract content without sending to AI
- Refactor useContentPanel into contentExtraction.ts and contentFiltering.ts
- Banner fallback composable for 3-stage image loading
- Wikipedia and Google Books as fallback image sources
- Loading skeletons with variant-specific shapes
- Mobile UX: auto-switch to content, back button, detail flow
- Project grid with breadcrumb nav and inline creation
- Filesystem Vite plugin for local project browsing
- Magazine text cleanup and song grid polish

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

packages/app/src/components/content/SongGrid.vue

@@ -51,10 +51,10 @@
           class="group flex flex-col items-stretch text-left w-full path-glass-bubble rounded-2xl overflow-hidden transition-all duration-200 hover:brightness-105"
           @click="$emit('selectSong', song)"
         >
-          <div class="cover-card flex-1 min-h-0 relative">
+          <div class="cover-card flex-1 min-h-0 relative flex items-center justify-center">
             <div class="aspect-square relative w-full overflow-hidden rounded-[10px]">
               <button
-                class="absolute inset-0 flex items-center justify-center z-10 backdrop-blur-sm bg-black/30 opacity-0 group-hover:opacity-100 transition-all duration-200"
+                class="absolute inset-0 bottom-10 flex items-center justify-center z-10 backdrop-blur-sm bg-black/30 opacity-0 group-hover:opacity-100 transition-all duration-200"
                 aria-label="Play"
                 @click.stop="onPlayClick(song)"
               >
@@ -97,10 +97,6 @@
               </div>
             </div>
           </div>
-          <p class="text-xs font-semibold mt-2 truncate px-0.5"
-             :class="isDark ? 'text-white/90' : 'text-gray-900'">
-            {{ song.title }}
-          </p>
         </button>
       </div>