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/ContextLoader.vue

@@ -22,7 +22,7 @@
           <slot name="header-actions" />
         </div>
       </div>
-      <LoadingFilmGrid :count="12" />
+      <LoadingContentGrid :variant="skeletonVariant" :count="skeletonCount" />
     </div>
 
     <div
@@ -71,7 +71,7 @@
 <script setup lang="ts">
 import { computed } from 'vue'
 import { useTheme } from '@/composables/useTheme'
-import LoadingFilmGrid from './LoadingFilmGrid.vue'
+import LoadingContentGrid from './LoadingContentGrid.vue'
 
 const props = withDefaults(
   defineProps<{
@@ -94,6 +94,19 @@ const contextLabel = computed(() => {
   if (props.contextType === 'magazine') return 'Brief'
   return 'Content'
 })
+
+const skeletonVariant = computed<'poster' | 'square' | 'list' | 'magazine'>(() => {
+  if (['song', 'podcast', 'image'].includes(props.contextType)) return 'square'
+  if (['news', 'websites'].includes(props.contextType)) return 'list'
+  if (props.contextType === 'magazine') return 'magazine'
+  return 'poster'
+})
+
+const skeletonCount = computed(() => {
+  if (props.contextType === 'magazine') return 6
+  if (['news', 'websites'].includes(props.contextType)) return 6
+  return 12
+})
 </script>
 
 <style scoped>