perf: 编写并执行数据库迁移，为 messages 表添加 (room_id, sent_at) 联合索引以消除慢查询

database/migrations/2026_06_30_114000_add_compound_index_to_messages_table.php

@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * 文件功能：为消息表（messages）添加 (room_id, sent_at) 联合复合索引
+ * 解决拉取房间聊天历史消息时的 Slow Query 瓶颈
+ *
+ * @author   ChatRoom Laravel
+ * @version  1.0.0
+ */
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * 执行迁移，添加联合索引
+     */
+    public function up(): void
+    {
+        Schema::table('messages', function (Blueprint $table) {
+            // 添加复合索引 idx_room_sent_at
+            $table->index(['room_id', 'sent_at'], 'idx_room_sent_at');
+        });
+    }
+
+    /**
+     * 回滚迁移，删除联合索引
+     */
+    public function down(): void
+    {
+        Schema::table('messages', function (Blueprint $table) {
+            $table->dropIndex('idx_room_sent_at');
+        });
+    }
+};