feat(content): add places, code mode, mobile context tab, and detail views

- Add Places/Restaurants content type with PlaceCard, PlaceDetail, PlaceGrid
- Add WebsiteDetail and MagazineSectionDetail views for Context panel
- Enhance MagazineGrid hero with background image and 3x taller header
- Add mobile 3-tab layout (Chat, Content, Context) with detail navigation
- Add /code command system: useCodeContext composable, ProjectGrid, FileTreeNode,
  CodeDetail for IDE-style code viewing across all three panels
- Fix /code bubble and prompt index clicks to re-activate code mode
- Fix updatePanelFromText overwriting code tab by skipping command messages

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

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

@@ -137,6 +137,9 @@
           :query="panelQuery"
           :hero-image="panelMagazineHeroImage ?? undefined"
         />
+        <ProjectGrid
+          v-else-if="activeTab === 'code'"
+        />
       </div>
     </aside>
   </Transition>
@@ -159,6 +162,7 @@ import PodcastDetail from './PodcastDetail.vue'
 import NewsGrid from './NewsGrid.vue'
 import ArticleDetail from './ArticleDetail.vue'
 import MagazineGrid from './MagazineGrid.vue'
+import ProjectGrid from './ProjectGrid.vue'
 
 const { isDark } = useTheme()
 const {
@@ -213,11 +217,13 @@ const TAB_LABELS: Record<ContentTab, string> = {
   book: 'Books',
   tvshow: 'TV',
   image: 'Images',
+  place: 'Places',
   song: 'Music',
   podcast: 'Podcasts',
   news: 'News',
   websites: 'Web',
   magazine: 'Brief',
+  code: 'Code',
 }
 
 function tabLabel(tab: ContentTab): string {