feat(ui): add drag-and-drop sorting for provider list (#126)

* feat(ui): add drag-and-drop sorting for provider list

Implement drag-and-drop functionality to allow users to reorder providers with custom sort indices.

Features:
- Install @dnd-kit libraries for drag-and-drop support
- Add sortIndex field to Provider type (frontend & backend)
- Implement SortableProviderItem component with drag handle
- Add update_providers_sort_order Tauri command
- Sync tray menu order with provider list sorting
- Add i18n support for drag-related UI text

Technical details:
- Use @dnd-kit/core and @dnd-kit/sortable for smooth drag interactions
- Disable animations for immediate response after drop
- Update tray menu immediately after reordering
- Sort priority: sortIndex → createdAt → name

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

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

* fix(ui): remove unused transition variable in ProviderList

Remove unused 'transition' destructured variable from useSortable hook
to fix TypeScript error TS6133. The transition property is hardcoded
as 'none' in the style object to prevent conflicts with drag operations.

---------

Co-authored-by: Claude <noreply@anthropic.com>

package.json

@@ -32,7 +32,9 @@
     "@codemirror/state": "^6.5.2",
     "@codemirror/theme-one-dark": "^6.1.3",
     "@codemirror/view": "^6.38.2",
-    "smol-toml": "^1.4.2",
+    "@dnd-kit/core": "^6.3.1",
+    "@dnd-kit/sortable": "^10.0.0",
+    "@dnd-kit/utilities": "^3.2.2",
     "@tailwindcss/vite": "^4.1.13",
     "@tauri-apps/api": "^2.8.0",
     "@tauri-apps/plugin-dialog": "^2.4.0",
@@ -46,6 +48,7 @@
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
     "react-i18next": "^16.0.0",
+    "smol-toml": "^1.4.2",
     "tailwindcss": "^4.1.13"
   }
 }