feat(ui): add dedicated Agent subagent rendering with nested tool call display

Render Agent/Explore/Plan tool calls in a visually distinct collapsible
container with colored left border, replacing the generic tool card. Parse
subagent JSONL transcripts from {sessionId}/subagents/ to extract and
display the actual tool calls (Bash, Read, Grep, etc.) the subagent
executed, reusing the existing ToolCallPart for consistent appearance.

- Add AgentToolCallPart component with collapsible body, prompt section,
  execution stats, and nested tool call list via render prop injection
- Add AgentExecutionStats and AgentToolCall types (Rust + TypeScript)
- Parse toolUseResult.agentId to locate and read subagent JSONL files
- Validate agentId against path traversal before filesystem access
- Pass agentStats through adapter for both ID-matched and positional
  tool result pairing
- Strip agentStats in nested render to prevent recursive Agent expansion
- Add i18n keys for agent UI labels across all 10 languages

src/i18n/messages/ar.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "الموضوع",
         "taskLabel": "المهمة",
         "nameLabel": "الاسم:",
+        "agentPromptLabel": "المطالبة",
+        "agentModelLabel": "النموذج",
+        "agentStatsBash": "الأوامر",
+        "agentStatsRead": "الملفات المقروءة",
+        "agentStatsSearch": "عمليات البحث",
+        "agentStatsEdit": "التعديلات",
+        "agentStatsOther": "أخرى",
         "field": {
           "file": "ملف",
           "notebook": "دفتر",

src/i18n/messages/de.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "Betreff",
         "taskLabel": "Aufgabe",
         "nameLabel": "Bezeichnung:",
+        "agentPromptLabel": "Eingabe",
+        "agentModelLabel": "Modell",
+        "agentStatsBash": "Befehle",
+        "agentStatsRead": "Dateien gelesen",
+        "agentStatsSearch": "Suchen",
+        "agentStatsEdit": "Bearbeitungen",
+        "agentStatsOther": "Sonstige",
         "field": {
           "file": "Datei",
           "notebook": "Notizbuch",

src/i18n/messages/en.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "Subject",
         "taskLabel": "Task",
         "nameLabel": "Name:",
+        "agentPromptLabel": "Prompt",
+        "agentModelLabel": "Model",
+        "agentStatsBash": "Commands",
+        "agentStatsRead": "Files read",
+        "agentStatsSearch": "Searches",
+        "agentStatsEdit": "Edits",
+        "agentStatsOther": "Other",
         "field": {
           "file": "File",
           "notebook": "Notebook",

src/i18n/messages/es.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "Asunto",
         "taskLabel": "Tarea",
         "nameLabel": "Nombre:",
+        "agentPromptLabel": "Instrucción",
+        "agentModelLabel": "Modelo",
+        "agentStatsBash": "Comandos",
+        "agentStatsRead": "Archivos leídos",
+        "agentStatsSearch": "Búsquedas",
+        "agentStatsEdit": "Ediciones",
+        "agentStatsOther": "Otros",
         "field": {
           "file": "Archivo",
           "notebook": "Cuaderno",

src/i18n/messages/fr.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "Sujet",
         "taskLabel": "Tâche",
         "nameLabel": "Nom :",
+        "agentPromptLabel": "Instruction",
+        "agentModelLabel": "Modèle",
+        "agentStatsBash": "Commandes",
+        "agentStatsRead": "Fichiers lus",
+        "agentStatsSearch": "Recherches",
+        "agentStatsEdit": "Modifications",
+        "agentStatsOther": "Autres",
         "field": {
           "file": "Fichier",
           "notebook": "Carnet",

src/i18n/messages/ja.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "件名",
         "taskLabel": "タスク",
         "nameLabel": "名前:",
+        "agentPromptLabel": "プロンプト",
+        "agentModelLabel": "モデル",
+        "agentStatsBash": "コマンド",
+        "agentStatsRead": "ファイル読取",
+        "agentStatsSearch": "検索",
+        "agentStatsEdit": "編集",
+        "agentStatsOther": "その他",
         "field": {
           "file": "ファイル",
           "notebook": "ノートブック",

src/i18n/messages/ko.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "제목",
         "taskLabel": "작업",
         "nameLabel": "이름:",
+        "agentPromptLabel": "프롬프트",
+        "agentModelLabel": "모델",
+        "agentStatsBash": "명령",
+        "agentStatsRead": "파일 읽기",
+        "agentStatsSearch": "검색",
+        "agentStatsEdit": "편집",
+        "agentStatsOther": "기타",
         "field": {
           "file": "파일",
           "notebook": "노트북",

src/i18n/messages/pt.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "Assunto",
         "taskLabel": "Tarefa",
         "nameLabel": "Nome:",
+        "agentPromptLabel": "Instrução",
+        "agentModelLabel": "Modelo",
+        "agentStatsBash": "Comandos",
+        "agentStatsRead": "Arquivos lidos",
+        "agentStatsSearch": "Pesquisas",
+        "agentStatsEdit": "Edições",
+        "agentStatsOther": "Outros",
         "field": {
           "file": "Arquivo",
           "notebook": "Caderno",

src/i18n/messages/zh-CN.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "主题",
         "taskLabel": "任务",
         "nameLabel": "名称：",
+        "agentPromptLabel": "提示词",
+        "agentModelLabel": "模型",
+        "agentStatsBash": "命令",
+        "agentStatsRead": "读取文件",
+        "agentStatsSearch": "搜索",
+        "agentStatsEdit": "编辑",
+        "agentStatsOther": "其他",
         "field": {
           "file": "文件",
           "notebook": "笔记本",

src/i18n/messages/zh-TW.json

@@ -1703,6 +1703,13 @@
         "subjectLabel": "主題",
         "taskLabel": "任務",
         "nameLabel": "名稱：",
+        "agentPromptLabel": "提示詞",
+        "agentModelLabel": "模型",
+        "agentStatsBash": "命令",
+        "agentStatsRead": "讀取檔案",
+        "agentStatsSearch": "搜尋",
+        "agentStatsEdit": "編輯",
+        "agentStatsOther": "其他",
         "field": {
           "file": "檔案",
           "notebook": "筆記本",