refactor(system): 重构消息中心功能

- 移除 WebSocket相关代码
- 新增 SSE (Server-Sent Events) 实现消息推送
- 优化消息中心未读数量展示和更新逻辑- 调整消息中心相关 API 和前端展示

backend/application/sse_views.py

@@ -0,0 +1,33 @@
+# views.py
+import time
+
+import jwt
+from django.http import StreamingHttpResponse
+
+from application import settings
+from dvadmin.system.models import MessageCenterTargetUser
+from django.core.cache import cache
+
+
+def event_stream(user_id):
+    last_sent_time = 0
+
+    while True:
+        # 从 Redis 中获取最后数据库变更时间
+        last_db_change_time = cache.get('last_db_change_time', 0)
+        # 只有当数据库发生变化时才检查总数
+        if last_db_change_time and last_db_change_time > last_sent_time:
+            count = MessageCenterTargetUser.objects.filter(users=user_id, is_read=False).count()
+            yield f"data: {count}\n\n"
+            last_sent_time = time.time()
+
+        time.sleep(1)
+
+
+def sse_view(request):
+    token = request.GET.get('token')
+    decoded = jwt.decode(token, settings.SECRET_KEY, algorithms=['HS256'])
+    user_id = decoded.get('user_id')
+    response = StreamingHttpResponse(event_stream(user_id), content_type='text/event-stream')
+    response['Cache-Control'] = 'no-cache'
+    return response