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>

src/i18n/locales/en.json

@@ -63,7 +63,9 @@
     "configError": "Configuration Error",
     "notConfigured": "Not configured for official website",
     "applyToClaudePlugin": "Apply to Claude plugin",
-    "removeFromClaudePlugin": "Remove from Claude plugin"
+    "removeFromClaudePlugin": "Remove from Claude plugin",
+    "dragToReorder": "Drag to reorder",
+    "sortUpdateFailed": "Failed to update sort order"
   },
   "notifications": {
     "providerSaved": "Provider configuration saved",

src/i18n/locales/zh.json

@@ -63,7 +63,9 @@
     "configError": "配置错误",
     "notConfigured": "未配置官网地址",
     "applyToClaudePlugin": "应用到 Claude 插件",
-    "removeFromClaudePlugin": "从 Claude 插件移除"
+    "removeFromClaudePlugin": "从 Claude 插件移除",
+    "dragToReorder": "拖拽以重新排序",
+    "sortUpdateFailed": "排序更新失败"
   },
   "notifications": {
     "providerSaved": "供应商配置已保存",