🔔 飞行侠实现：实例注册 + Webhook 推送

新功能:
- instances 应用：OpenClaw 实例管理
- Instance 模型：实例注册，Agent 列表，Webhook URL
- MeetingInstanceMap：会议 - 实例映射
- Webhook 推送：消息发送时自动通知相关实例

API 端点:
- POST /api/v1/instances/register/ - 实例注册
- POST /api/v1/instances/join-meeting/ - 加入会议
- GET  /api/v1/instances/ - 实例列表
- POST /api/v1/instances/webhook-test/ - Webhook 测试

集成:
- send_message API 自动触发 Webhook 推送
- 支持广播和定向推送

测试:
- test_webhook.py: 完整测试流程

使用场景:
1. 每台 OpenClaw 机器注册实例
2. Agent 加入会议时关联实例
3. 消息发送时推送到对应机器
4. 本机 OpenClaw 收到通知，触发 Agent 响应

backend/instances/migrations/0001_initial.py

@@ -0,0 +1,110 @@
+# Generated by Django 6.0.3 on 2026-04-04 04:02
+
+import django.db.models.deletion
+import uuid
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="Instance",
+            fields=[
+                (
+                    "id",
+                    models.UUIDField(
+                        default=uuid.uuid4,
+                        editable=False,
+                        primary_key=True,
+                        serialize=False,
+                    ),
+                ),
+                (
+                    "instance_id",
+                    models.CharField(
+                        max_length=100, unique=True, verbose_name="实例 ID"
+                    ),
+                ),
+                (
+                    "instance_name",
+                    models.CharField(max_length=200, verbose_name="实例名称"),
+                ),
+                (
+                    "agent_ids",
+                    models.JSONField(default=list, verbose_name="Agent ID 列表"),
+                ),
+                (
+                    "webhook_url",
+                    models.URLField(
+                        help_text="消息推送地址", verbose_name="Webhook URL"
+                    ),
+                ),
+                (
+                    "webhook_enabled",
+                    models.BooleanField(default=True, verbose_name="启用 Webhook"),
+                ),
+                (
+                    "is_active",
+                    models.BooleanField(default=True, verbose_name="是否活跃"),
+                ),
+                (
+                    "last_heartbeat",
+                    models.DateTimeField(
+                        blank=True, null=True, verbose_name="最后心跳"
+                    ),
+                ),
+                ("created_at", models.DateTimeField(auto_now_add=True)),
+                ("updated_at", models.DateTimeField(auto_now=True)),
+            ],
+            options={
+                "verbose_name": "OpenClaw 实例",
+                "verbose_name_plural": "OpenClaw 实例",
+                "db_table": "instances",
+                "ordering": ["-created_at"],
+            },
+        ),
+        migrations.CreateModel(
+            name="MeetingInstanceMap",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("meeting_id", models.UUIDField(verbose_name="会议 ID")),
+                (
+                    "agent_ids",
+                    models.JSONField(default=list, verbose_name="参与的 Agent ID 列表"),
+                ),
+                ("joined_at", models.DateTimeField(auto_now_add=True)),
+                ("left_at", models.DateTimeField(blank=True, null=True)),
+                (
+                    "instance",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="meetings",
+                        to="instances.instance",
+                    ),
+                ),
+            ],
+            options={
+                "db_table": "meeting_instance_maps",
+                "indexes": [
+                    models.Index(
+                        fields=["meeting_id", "left_at"],
+                        name="meeting_ins_meeting_947179_idx",
+                    )
+                ],
+                "unique_together": {("meeting_id", "instance")},
+            },
+        ),
+    ]