feat(layout): Replace top navbar with sidebar layout

- Add new sidebar-based layout components:
  - AppLayout.vue: Main layout wrapper with sidebar + topbar
  - AppSidebar.vue: Desktop sidebar with navigation, theme, language
  - AppTopBar.vue: Top bar with notifications, cart, profile
  - MobileDrawer.vue: Slide-out drawer for mobile navigation
- Add Shadcn Sheet component for mobile drawer
- Update App.vue to use new AppLayout (except login page)
- Rename old Navbar.vue to Navbar.old.vue for reference

Layout structure:
- Desktop: Fixed 288px sidebar + offset content area
- Mobile: Hidden sidebar with drawer triggered from top bar
- Cart only shown when market module is enabled
- Combined notifications (chat unread count)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -34,7 +34,7 @@
     "qr-scanner": "^1.4.2",
     "qrcode": "^1.5.4",
     "radix-vue": "^1.9.13",
-    "reka-ui": "^2.5.0",
+    "reka-ui": "^2.7.0",
     "tailwind-merge": "^2.6.0",
     "tailwindcss-animate": "^1.0.7",
     "unique-names-generator": "^4.7.1",