feat: use Task tool description for subagent window titles + auto-minimize completed

- Extract short description from TaskTracker (params.description) for subagent windows
- Correlate subagents with sessions by working directory and timing
- Auto-minimize subagent windows when agents complete
- Persist minimized/open window states to server for cross-browser sync
- Restore window states on reconnection/page reload
- New API: GET/PUT /api/subagent-window-states
- State file: ~/.claudeman/subagent-window-states.json

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/run-summary.ts

@@ -184,7 +184,9 @@ export class RunSummaryTracker {
     const now = Date.now();
 
     // Update idle time if was previously idle
-    if (!this.isCurrentlyActive && this.stats.lastIdleAt) {
+    // Note: We count the initial idle period (from session start to first working state)
+    // even if lastIdleAt hasn't been set yet
+    if (!this.isCurrentlyActive) {
       this.stats.totalTimeIdleMs += now - this.lastStatusChangeAt;
     }