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/core/src/types/content.ts

@@ -137,3 +137,29 @@ export interface ImageItem {
   source?: string
   attribution?: string
 }
+
+export interface Place {
+  id: string
+  name: string
+  address?: string
+  city?: string
+  cuisine?: string
+  category?: string
+  rating?: number
+  priceLevel?: number // 1-4 ($-$$$$)
+  phone?: string
+  website?: string
+  hours?: string
+  description?: string
+  photoUrl?: string
+  lat?: number
+  lng?: number
+  sources?: PlaceSource[]
+}
+
+export interface PlaceSource {
+  type: 'gmaps' | 'osm' | 'yelp' | 'tripadvisor' | 'foursquare' | 'local'
+  name: string
+  url: string
+  icon?: string
+}