feat: parallel session creation and improved minimized agents UI

- Session creation now parallelized (3x faster for multiple tabs)
- Minimized agents badge: compact, hover-triggered, auto-hide
- Removed "Minimized Agents" header, status dots instead of text
- Click to pin dropdown open, hover for quick access

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

src/session.ts

@@ -1424,11 +1424,16 @@ export class Session extends EventEmitter {
    */
   private cleanupOldTaskDescriptions(): void {
     const cutoff = Date.now() - Session.TASK_DESCRIPTION_MAX_AGE_MS;
+    // Collect keys to delete first, then delete (avoids modifying Map during iteration)
+    const keysToDelete: number[] = [];
     for (const [timestamp] of this._recentTaskDescriptions) {
       if (timestamp < cutoff) {
-        this._recentTaskDescriptions.delete(timestamp);
+        keysToDelete.push(timestamp);
       }
     }
+    for (const key of keysToDelete) {
+      this._recentTaskDescriptions.delete(key);
+    }
 
     // Enforce size limit by removing oldest entries
     if (this._recentTaskDescriptions.size > Session.MAX_TASK_DESCRIPTIONS) {