feat: add provider duplicate functionality in edit mode

Add a duplicate button next to the drag handle in edit mode that allows users to quickly copy existing provider configurations.

- Add Copy icon button in ProviderCard next to drag handle
- Implement handleDuplicateProvider in App.tsx with deep cloning
- Copy all provider settings (settingsConfig, websiteUrl, category, meta)
- Auto-generate new ID and timestamp, omit sortIndex for natural sorting
- Append " copy" to duplicated provider name
- Add i18n support (zh: "复制", en: "Duplicate")
- Wire onDuplicate callback through ProviderList to ProviderCard

The duplicated provider will appear below the original provider in the list, sorted by creation time.

src/components/providers/ProviderList.tsx

@@ -20,6 +20,7 @@ interface ProviderListProps {
   onSwitch: (provider: Provider) => void;
   onEdit: (provider: Provider) => void;
   onDelete: (provider: Provider) => void;
+  onDuplicate: (provider: Provider) => void;
   onConfigureUsage?: (provider: Provider) => void;
   onOpenWebsite: (url: string) => void;
   onCreate?: () => void;
@@ -34,6 +35,7 @@ export function ProviderList({
   onSwitch,
   onEdit,
   onDelete,
+  onDuplicate,
   onConfigureUsage,
   onOpenWebsite,
   onCreate,
@@ -82,6 +84,7 @@ export function ProviderList({
               onSwitch={onSwitch}
               onEdit={onEdit}
               onDelete={onDelete}
+              onDuplicate={onDuplicate}
               onConfigureUsage={onConfigureUsage}
               onOpenWebsite={onOpenWebsite}
             />
@@ -100,6 +103,7 @@ interface SortableProviderCardProps {
   onSwitch: (provider: Provider) => void;
   onEdit: (provider: Provider) => void;
   onDelete: (provider: Provider) => void;
+  onDuplicate: (provider: Provider) => void;
   onConfigureUsage?: (provider: Provider) => void;
   onOpenWebsite: (url: string) => void;
 }
@@ -112,6 +116,7 @@ function SortableProviderCard({
   onSwitch,
   onEdit,
   onDelete,
+  onDuplicate,
   onConfigureUsage,
   onOpenWebsite,
 }: SortableProviderCardProps) {
@@ -139,6 +144,7 @@ function SortableProviderCard({
         onSwitch={onSwitch}
         onEdit={onEdit}
         onDelete={onDelete}
+        onDuplicate={onDuplicate}
         onConfigureUsage={
           onConfigureUsage ? (item) => onConfigureUsage(item) : () => undefined
         }