refactor(ui): reorganize components into ui/ subdirectory and share layout

- Move shadcn components from src/components/ to src/components/ui/
- Move component-example and example from apps/web to packages/ui
- Update package.json exports with separate components/* and components/ui/* paths
- Update components.json ui alias in both packages/ui and apps/web
- Add missing @import "shadcn/tailwind.css" to globals.css
- Add new UI components: sheet, sidebar, skeleton, switch
- Update apps/web and apps/desktop to use shared ComponentExample

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

apps/web/components.json

@@ -15,7 +15,7 @@
     "hooks": "@/hooks",
     "lib": "@/lib",
     "utils": "@multica/ui/lib/utils",
-    "ui": "@multica/ui/components"
+    "ui": "@multica/ui/components/ui"
   },
   "menuColor": "default",
   "menuAccent": "subtle"