fix: broadcast state change after redraw current round

Add emit('stateChange') to notify frontend clients when
lottery round is redrawn, so UI updates correctly.

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

packages/server/src/services/admin.service.ts

@@ -521,6 +521,9 @@ class AdminService extends EventEmitter {
       this.state.lottery.currentWinners = [];
 
       await this.saveState();
+      // Broadcast state change to all clients
+      this.emit('stateChange', this.getState());
+
       logger.warn({ round: currentRound, clearedWinners: winnersToRemove.length }, 'Current round redrawn');
 
       return { success: true, message: `第${currentRound}轮已重置，可重新抽取` };