feat: add skill storage location toggle between CC Switch and ~/.agents/skills

Allow users to choose between storing skills in CC Switch's managed
directory (~/.cc-switch/skills/) or the Agent Skills open standard
directory (~/.agents/skills/). Includes migration logic that safely
moves files before updating settings, with confirmation dialog for
non-empty installations.

src/i18n/locales/en.json

@@ -478,6 +478,18 @@
       "geminiDesc": "Google Gemini CLI",
       "opencodeDesc": "OpenCode CLI"
     },
+    "skillStorage": {
+      "title": "Skill Storage Location",
+      "description": "Choose where CC Switch stores the master copies of your skills",
+      "ccSwitch": "CC Switch",
+      "unified": "~/.agents/skills",
+      "ccSwitchHint": "Skills are stored in ~/.cc-switch/skills/ and synced to each app via symlink or copy.",
+      "unifiedHint": "Skills are stored in ~/.agents/skills/, the Agent Skills open standard. Compatible tools (Claude Code, Codex, Gemini CLI, etc.) discover skills here natively.",
+      "confirmTitle": "Migrate Skill Storage",
+      "confirmMessage": "{{count}} skill(s) will be moved to the new location. Continue?",
+      "migrationSuccess": "Successfully migrated {{count}} skill(s)",
+      "migrationPartial": "Migrated {{migrated}} skill(s), {{errors}} error(s). Check logs for details."
+    },
     "skillSync": {
       "title": "Skill Sync Method",
       "description": "Choose how to sync Skills files",

src/i18n/locales/ja.json

@@ -478,6 +478,18 @@
       "geminiDesc": "Google Gemini CLI",
       "opencodeDesc": "OpenCode CLI"
     },
+    "skillStorage": {
+      "title": "スキル保存場所",
+      "description": "CC Switch がスキルのマスターコピーを保存するディレクトリを選択します",
+      "ccSwitch": "CC Switch",
+      "unified": "~/.agents/skills",
+      "ccSwitchHint": "スキルは ~/.cc-switch/skills/ に保存され、シンボリックリンクまたはコピーで各アプリに同期されます。",
+      "unifiedHint": "スキルは ~/.agents/skills/ に保存されます（Agent Skills オープン標準）。対応ツール（Claude Code、Codex、Gemini CLI など）はこのディレクトリのスキルを直接検出します。",
+      "confirmTitle": "スキル保存場所の移行",
+      "confirmMessage": "{{count}} 個のスキルを新しい場所に移動します。続行しますか？",
+      "migrationSuccess": "{{count}} 個のスキルを移行しました",
+      "migrationPartial": "{{migrated}} 個のスキルを移行、{{errors}} 個のエラー。詳細はログを確認してください。"
+    },
     "skillSync": {
       "title": "スキル同期方式",
       "description": "スキルファイルの同期方法を選択",

src/i18n/locales/zh.json

@@ -478,6 +478,18 @@
       "geminiDesc": "Google Gemini CLI",
       "opencodeDesc": "OpenCode CLI"
     },
+    "skillStorage": {
+      "title": "技能存储位置",
+      "description": "选择 CC Switch 存放技能主副本的目录",
+      "ccSwitch": "CC Switch",
+      "unified": "~/.agents/skills",
+      "ccSwitchHint": "技能存储在 ~/.cc-switch/skills/，由 CC Switch 统一管理并同步到各应用。",
+      "unifiedHint": "技能存储在 ~/.agents/skills/，遵循 Agent Skills 开放标准。兼容的工具（Claude Code、Codex、Gemini CLI 等）可直接发现此目录中的技能。",
+      "confirmTitle": "迁移技能存储",
+      "confirmMessage": "将移动 {{count}} 个技能到新位置，是否继续？",
+      "migrationSuccess": "已成功迁移 {{count}} 个技能",
+      "migrationPartial": "迁移了 {{migrated}} 个技能，{{errors}} 个失败，请查看日志"
+    },
     "skillSync": {
       "title": "Skill 同步方式",
       "description": "选择 Skills 的文件同步策略",