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/web/server.ts

@@ -3292,8 +3292,8 @@ export class WebServer extends EventEmitter {
       this.scheduledCleanupTimer = null;
     }
 
-    // Stop screen stats collection
-    this.screenManager.stopStatsCollection();
+    // Stop screen manager and flush pending saves
+    this.screenManager.destroy();
 
     // Clear all pending respawn start timers (from restoration grace period)
     for (const timer of this.pendingRespawnStarts.values()) {