feat: add edit mode toggle to show/hide drag handles

- Add edit mode button next to settings in header
- Edit button turns blue when active
- Drag handles fade in/out with edit mode toggle
- Add smooth 200ms transition animation
- Add i18n support for edit mode (en/zh)
- Maintain consistent spacing between header elements

src/i18n/locales/en.json

@@ -47,7 +47,9 @@
     "toggleLightMode": "Switch to Light Mode",
     "addProvider": "Add Provider",
     "switchToChinese": "Switch to Chinese",
-    "switchToEnglish": "Switch to English"
+    "switchToEnglish": "Switch to English",
+    "enterEditMode": "Enter Edit Mode",
+    "exitEditMode": "Exit Edit Mode"
   },
   "provider": {
     "noProviders": "No providers added yet",