feat: sub-agent streaming progress — TaskTool emits real-time status events

- Rust: LoopEvent::SubtaskStatus variant added to loop_runner.rs
- Rust: ToolContext.event_sender field for streaming tool progress
- Rust: TaskTool emits started/running/completed/failed via event_sender
- Rust: StreamChatEvent::SubtaskStatus mapped in Tauri chat command
- TS: StreamEventSubtaskStatus type + onSubtaskStatus callback added
- TS: kernel-chat.ts handles subtaskStatus event from Tauri
- TS: streamStore.ts wires callback, maps backend→frontend status,
  updates assistant message subtasks array in real-time

crates/zclaw-runtime/src/loop_runner.rs

@@ -206,6 +206,7 @@ impl AgentLoop {
             session_id: Some(session_id.to_string()),
             skill_executor: self.skill_executor.clone(),
             path_validator: Some(path_validator),
+            event_sender: None,
         }
     }
 
@@ -880,6 +881,7 @@ impl AgentLoop {
                                     session_id: Some(session_id_clone.to_string()),
                                     skill_executor: skill_executor.clone(),
                                     path_validator: Some(pv),
+                                    event_sender: Some(tx.clone()),
                                 };
                                 let (result, is_error) = if let Some(tool) = tools.get(&name) {
                                     match tool.execute(new_input, &tool_context).await {
@@ -945,6 +947,7 @@ impl AgentLoop {
                         session_id: Some(session_id_clone.to_string()),
                         skill_executor: skill_executor.clone(),
                         path_validator: Some(pv),
+                        event_sender: Some(tx.clone()),
                     };
 
                     let (result, is_error) = if let Some(tool) = tools.get(&name) {
@@ -1008,6 +1011,12 @@ pub enum LoopEvent {
     ToolStart { name: String, input: serde_json::Value },
     /// Tool execution completed
     ToolEnd { name: String, output: serde_json::Value },
+    /// Sub-agent task status update (started/running/completed/failed)
+    SubtaskStatus {
+        description: String,
+        status: String,
+        detail: Option<String>,
+    },
     /// New iteration started (multi-turn tool calling)
     IterationStart { iteration: usize, max_iterations: usize },
     /// Loop completed with final result