feat(skills): add skill sync method setting (symlink/copy)

- Add SyncMethod enum (Auto/Symlink/Copy) in Rust backend
- Implement sync_to_app_dir with symlink support (cross-platform)
- Add SkillSyncMethodSettings UI component (simplified 2-button selector)
- Add i18n support for zh/en/ja
- Replace copy_to_app with configurable sync_to_app_dir
- Add skill_sync_method field to AppSettings

User can now choose between symlink (disk space saving) or copy (best compatibility) in Settings > General.

src/components/providers/forms/hooks/useModelState.ts

@@ -51,19 +51,19 @@ export function useModelState({
 }: UseModelStateProps) {
   // Initialize state by parsing config directly (fixes edit mode backfill)
   const [claudeModel, setClaudeModel] = useState(
-    () => parseModelsFromConfig(settingsConfig).model
+    () => parseModelsFromConfig(settingsConfig).model,
   );
   const [reasoningModel, setReasoningModel] = useState(
-    () => parseModelsFromConfig(settingsConfig).reasoning
+    () => parseModelsFromConfig(settingsConfig).reasoning,
   );
   const [defaultHaikuModel, setDefaultHaikuModel] = useState(
-    () => parseModelsFromConfig(settingsConfig).haiku
+    () => parseModelsFromConfig(settingsConfig).haiku,
   );
   const [defaultSonnetModel, setDefaultSonnetModel] = useState(
-    () => parseModelsFromConfig(settingsConfig).sonnet
+    () => parseModelsFromConfig(settingsConfig).sonnet,
   );
   const [defaultOpusModel, setDefaultOpusModel] = useState(
-    () => parseModelsFromConfig(settingsConfig).opus
+    () => parseModelsFromConfig(settingsConfig).opus,
   );
 
   const isUserEditingRef = useRef(false);

src/components/settings/SettingsPage.tsx

@@ -35,6 +35,7 @@ import { LanguageSettings } from "@/components/settings/LanguageSettings";
 import { ThemeSettings } from "@/components/settings/ThemeSettings";
 import { WindowSettings } from "@/components/settings/WindowSettings";
 import { AppVisibilitySettings } from "@/components/settings/AppVisibilitySettings";
+import { SkillSyncMethodSettings } from "@/components/settings/SkillSyncMethodSettings";
 import { DirectorySettings } from "@/components/settings/DirectorySettings";
 import { ImportExportSection } from "@/components/settings/ImportExportSection";
 import { AboutSection } from "@/components/settings/AboutSection";
@@ -249,6 +250,12 @@ export function SettingsPage({
                     settings={settings}
                     onChange={handleAutoSave}
                   />
+                  <SkillSyncMethodSettings
+                    value={settings.skillSyncMethod ?? "auto"}
+                    onChange={(method) =>
+                      handleAutoSave({ skillSyncMethod: method })
+                    }
+                  />
                 </motion.div>
               ) : null}
             </TabsContent>

src/components/settings/SkillSyncMethodSettings.tsx

@@ -0,0 +1,78 @@
+import { useTranslation } from "react-i18next";
+import { Button } from "@/components/ui/button";
+import { cn } from "@/lib/utils";
+import type { SkillSyncMethod } from "@/types";
+
+export interface SkillSyncMethodSettingsProps {
+  value: SkillSyncMethod;
+  onChange: (value: SkillSyncMethod) => void;
+}
+
+export function SkillSyncMethodSettings({
+  value,
+  onChange,
+}: SkillSyncMethodSettingsProps) {
+  const { t } = useTranslation();
+
+  // Handle default values: undefined or "auto" defaults to symlink display
+  const displayValue = value === "copy" ? "copy" : "symlink";
+
+  return (
+    <section className="space-y-2">
+      <header className="space-y-1">
+        <h3 className="text-sm font-medium">{t("settings.skillSync.title")}</h3>
+        <p className="text-xs text-muted-foreground">
+          {t("settings.skillSync.description")}
+        </p>
+      </header>
+      <div className="inline-flex gap-1 rounded-md border border-border-default bg-background p-1">
+        <SyncMethodButton
+          active={displayValue === "symlink"}
+          onClick={() => onChange("symlink")}
+        >
+          {t("settings.skillSync.symlink")}
+        </SyncMethodButton>
+        <SyncMethodButton
+          active={displayValue === "copy"}
+          onClick={() => onChange("copy")}
+        >
+          {t("settings.skillSync.copy")}
+        </SyncMethodButton>
+      </div>
+      {displayValue === "symlink" && (
+        <p className="text-xs text-muted-foreground">
+          {t("settings.skillSync.symlinkHint")}
+        </p>
+      )}
+    </section>
+  );
+}
+
+interface SyncMethodButtonProps {
+  active: boolean;
+  onClick: () => void;
+  children: React.ReactNode;
+}
+
+function SyncMethodButton({
+  active,
+  onClick,
+  children,
+}: SyncMethodButtonProps) {
+  return (
+    <Button
+      type="button"
+      onClick={onClick}
+      size="sm"
+      variant={active ? "default" : "ghost"}
+      className={cn(
+        "min-w-[96px]",
+        active
+          ? "shadow-sm"
+          : "text-muted-foreground hover:text-foreground hover:bg-muted",
+      )}
+    >
+      {children}
+    </Button>
+  );
+}