feat(tui): add usage overlay and sidebar for displaying usage statistics and tasks

feat(tui): implement status bar with connection and turn state indicators
feat(tui): create workflow panel for agent status and progress visualization
feat(web): introduce web frontend interface with static file serving
feat(ws): add WebSocket interface for real-time communication and session management

apps/infrastructure/src/subagent/workspace.rs

@@ -0,0 +1,10 @@
+//! Subagent workspace management — create isolated workspaces for subagents.
+
+use std::path::PathBuf;
+
+/// Create an isolated workspace directory for a subagent.
+pub fn create_subagent_workspace(base_dir: &PathBuf, agent_id: &str) -> anyhow::Result<PathBuf> {
+    let ws = base_dir.join("subagent-workspaces").join(agent_id);
+    std::fs::create_dir_all(&ws)?;
+    Ok(ws)
+}