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/parsers/openclaw.rs

@@ -1053,6 +1053,7 @@ fn extract_tool_result_content(value: &serde_json::Value) -> Vec<ContentBlock> {
         tool_use_id,
         output_preview: output,
         is_error,
+        agent_stats: None,
     });
 
     blocks
@@ -1238,7 +1239,7 @@ mod tests {
         assert_eq!(blocks.len(), 1);
         assert!(matches!(
             &blocks[0],
-            ContentBlock::ToolResult { tool_use_id, output_preview, is_error }
+            ContentBlock::ToolResult { tool_use_id, output_preview, is_error, .. }
             if tool_use_id.as_deref() == Some("call_123")
                 && output_preview.as_deref() == Some("file contents here")
                 && !is_error