feat(codex-skills): surface built-in .system skills as read-only

Scan ~/.codex/skills/.system so Codex CLI's bundled skills (imagegen,
skill-creator, etc.) appear in the $ autocomplete and Skills settings.
Mark them read_only on the API; the save/delete handlers refuse writes
to that path, and the UI shows a system badge with a tooltip and
disables edit/delete/save for those entries.

src/i18n/messages/ar.json

@@ -302,6 +302,8 @@
     "loadingSkill": "جارٍ تحميل Skill...",
     "emptyNoAgents": "لا يوجد وكيل متاح.",
     "noSelectionHint": "اختر Skill من اليسار، أو انقر على \"Skill جديد\" لإنشاء واحد.",
+    "systemBadge": "نظام",
+    "systemHint": "Skill مدمج في CLI · للقراءة فقط",
     "scope": {
       "global": "عام",
       "folder": "مجلد",

src/i18n/messages/de.json

@@ -302,6 +302,8 @@
     "loadingSkill": "Skill wird geladen...",
     "emptyNoAgents": "Kein verfügbarer Agent.",
     "noSelectionHint": "Wählen Sie links einen Skill oder klicken Sie auf „Neuer Skill“, um einen zu erstellen.",
+    "systemBadge": "System",
+    "systemHint": "Integrierter CLI-Skill · schreibgeschützt",
     "scope": {
       "global": "Global",
       "folder": "Ordner",

src/i18n/messages/en.json

@@ -302,6 +302,8 @@
     "loadingSkill": "Loading skill...",
     "emptyNoAgents": "No available agent.",
     "noSelectionHint": "Select a skill on the left, or click \"New Skill\" to create one.",
+    "systemBadge": "System",
+    "systemHint": "Built-in CLI skill · read-only",
     "scope": {
       "global": "Global",
       "folder": "Folder",

src/i18n/messages/es.json

@@ -302,6 +302,8 @@
     "loadingSkill": "Cargando Skill...",
     "emptyNoAgents": "No hay agentes disponibles.",
     "noSelectionHint": "Selecciona un Skill a la izquierda o haz clic en \"Nuevo Skill\" para crear uno.",
+    "systemBadge": "Sistema",
+    "systemHint": "Skill integrado del CLI · solo lectura",
     "scope": {
       "global": "Global",
       "folder": "Carpeta",

src/i18n/messages/fr.json

@@ -302,6 +302,8 @@
     "loadingSkill": "Chargement de la Skill...",
     "emptyNoAgents": "Aucun agent disponible.",
     "noSelectionHint": "Sélectionnez un Skill à gauche ou cliquez sur « Nouveau Skill » pour en créer un.",
+    "systemBadge": "Système",
+    "systemHint": "Skill intégré du CLI · lecture seule",
     "scope": {
       "global": "Global",
       "folder": "Dossier",

src/i18n/messages/ja.json

@@ -302,6 +302,8 @@
     "loadingSkill": "Skillを読み込み中...",
     "emptyNoAgents": "利用可能なエージェントがありません。",
     "noSelectionHint": "左側から Skill を選択するか、「新規 Skill」をクリックして作成してください。",
+    "systemBadge": "システム",
+    "systemHint": "CLI 組み込み Skill・読み取り専用",
     "scope": {
       "global": "グローバル",
       "folder": "フォルダ",

src/i18n/messages/ko.json

@@ -302,6 +302,8 @@
     "loadingSkill": "Skill 불러오는 중...",
     "emptyNoAgents": "사용 가능한 에이전트가 없습니다.",
     "noSelectionHint": "왼쪽에서 Skill을 선택하거나 \"새 Skill\"을 클릭하여 만드세요.",
+    "systemBadge": "시스템",
+    "systemHint": "CLI 내장 Skill · 읽기 전용",
     "scope": {
       "global": "전역",
       "folder": "폴더",

src/i18n/messages/pt.json

@@ -302,6 +302,8 @@
     "loadingSkill": "Carregando Skill...",
     "emptyNoAgents": "Nenhum agente disponível.",
     "noSelectionHint": "Selecione um Skill à esquerda ou clique em \"Novo Skill\" para criar um.",
+    "systemBadge": "Sistema",
+    "systemHint": "Skill integrado do CLI · somente leitura",
     "scope": {
       "global": "Global",
       "folder": "Pasta",

src/i18n/messages/zh-CN.json

@@ -302,6 +302,8 @@
     "loadingSkill": "正在加载 Skill...",
     "emptyNoAgents": "暂无可用 Agent。",
     "noSelectionHint": "从左侧选择一个 Skill，或点击“新建 Skill”创建。",
+    "systemBadge": "系统",
+    "systemHint": "CLI 内置 Skill · 只读",
     "scope": {
       "global": "全局",
       "folder": "文件夹",

src/i18n/messages/zh-TW.json

@@ -302,6 +302,8 @@
     "loadingSkill": "正在載入 Skill...",
     "emptyNoAgents": "暫無可用 Agent。",
     "noSelectionHint": "從左側選擇一個 Skill，或點擊「新建 Skill」建立。",
+    "systemBadge": "系統",
+    "systemHint": "CLI 內建 Skill · 唯讀",
     "scope": {
       "global": "全域",
       "folder": "資料夾",