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-tauri/src/models/message.rs

@@ -10,6 +10,48 @@ pub enum MessageRole {
     Tool,
 }
 
+/// A single tool call record from a subagent's execution transcript.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AgentToolCall {
+    pub tool_name: String,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub input_preview: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub output_preview: Option<String>,
+    pub is_error: bool,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AgentExecutionStats {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub agent_type: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub status: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub total_duration_ms: Option<u64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub total_tokens: Option<u64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub total_tool_use_count: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub read_count: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub search_count: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub bash_count: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub edit_file_count: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub lines_added: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub lines_removed: Option<u32>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub other_tool_count: Option<u32>,
+    /// Tool calls extracted from the subagent's own JSONL transcript.
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
+    pub tool_calls: Vec<AgentToolCall>,
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(tag = "type", rename_all = "snake_case")]
 pub enum ContentBlock {
@@ -31,6 +73,8 @@ pub enum ContentBlock {
         tool_use_id: Option<String>,
         output_preview: Option<String>,
         is_error: bool,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        agent_stats: Option<AgentExecutionStats>,
     },
     Thinking {
         text: String,

src-tauri/src/models/mod.rs

@@ -15,7 +15,10 @@ pub use conversation::{
     SidebarData,
 };
 pub use folder::{FolderCommandInfo, FolderDetail, FolderHistoryEntry, OpenedConversation};
-pub use message::{ContentBlock, MessageRole, MessageTurn, TurnRole, TurnUsage, UnifiedMessage};
+pub use message::{
+    AgentExecutionStats, AgentToolCall, ContentBlock, MessageRole, MessageTurn, TurnRole,
+    TurnUsage, UnifiedMessage,
+};
 pub use system::{
     GitCredentials, GitDetectResult, GitHubAccountsSettings, GitHubTokenValidation, GitSettings,
     SystemLanguageSettings, SystemProxySettings,