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/components/providers/ProviderCard.tsx

@@ -21,6 +21,7 @@ interface ProviderCardProps {
   provider: Provider;
   isCurrent: boolean;
   appType: AppType;
+  isEditMode?: boolean;
   onSwitch: (provider: Provider) => void;
   onEdit: (provider: Provider) => void;
   onDelete: (provider: Provider) => void;
@@ -59,6 +60,7 @@ export function ProviderCard({
   provider,
   isCurrent,
   appType,
+  isEditMode = false,
   onSwitch,
   onEdit,
   onDelete,
@@ -101,7 +103,10 @@ export function ProviderCard({
           <button
             type="button"
             className={cn(
-              "mt-1 flex h-8 w-8 items-center justify-center rounded-md border border-transparent text-muted-foreground transition-colors hover:border-muted hover:text-foreground",
+              "mt-1 flex h-8 w-8 flex-shrink-0 items-center justify-center rounded-md border text-muted-foreground transition-all duration-200",
+              isEditMode
+                ? "border-muted hover:border-primary hover:text-foreground opacity-100"
+                : "border-transparent opacity-0 pointer-events-none",
               dragHandleProps?.isDragging && "border-primary text-primary",
             )}
             aria-label={t("provider.dragHandle")}