fix: 修复P2P主题别名订阅的兼容性问题

1. 订阅重复检查新增Original与RcptTo匹配判断，避免别名订阅误判已订阅
2. 重构订阅get查询处理逻辑，提取为独立函数
3. 针对P2P别名订阅场景返回200响应而非304，帮助客户端完成别名到标准主题名的重命名，避免发布失败
4. 优化群摘要接口的权限校验和异常处理逻辑

server/im_http.go

@@ -5944,17 +5944,40 @@ func serveIMGroupSummary(wrt http.ResponseWriter, req *http.Request, topic strin
 		writeIMError(wrt, req, http.StatusMethodNotAllowed, 30002, imReasonMethodNotAllowed, "method not allowed", nil)
 		return
 	}
-	principal, selfSub, ok := requireIMGroupMember(wrt, req, topic, true)
+	principal, ok := authenticateIMHTTPBearer(wrt, req)
 	if !ok {
 		return
 	}
+	if types.GetTopicCat(topic) != types.TopicCatGrp {
+		writeIMError(wrt, req, http.StatusBadRequest, 30000, imReasonMalformedRequest, "malformed request", map[string]any{"field": "topic"})
+		return
+	}
+	// 已解散的群按文档约定对客户端表现为不存在（RESOURCE_NOT_FOUND），不暴露解散状态。
+	if settings, err := store.GroupBusiness.GetSettings(principal.TenantID, topic); err == nil &&
+		settings != nil && settings.GroupStatus == types.GroupStatusDissolved {
+		writeIMError(wrt, req, http.StatusNotFound, 30004, imReasonResourceNotFound, "group not found", nil)
+		return
+	}
+	selfSub, err := store.Subs.Get(principal.TenantID, topic, principal.Uid, false)
+	if err != nil {
+		writeIMError(wrt, req, http.StatusInternalServerError, 90000, imReasonInternal, "internal error", nil)
+		return
+	}
+	access := types.ModeNone
+	if selfSub != nil {
+		access = selfSub.ModeGiven & selfSub.ModeWant
+	}
+	if selfSub == nil || !access.IsJoiner() || !access.IsReader() {
+		writeIMError(wrt, req, http.StatusForbidden, 30005, imReasonPermissionDenied, "topic permission required", nil)
+		return
+	}
 	requests, _, _ := store.GroupBusiness.ListJoinRequests(principal.TenantID, topic, types.GroupJoinRequestStatusPending, "", 100)
 	announcement, _ := store.GroupBusiness.LatestAnnouncement(principal.TenantID, topic)
 	writeIMSuccess(wrt, req, map[string]any{
 		"topic":                      topic,
 		"pending_join_request_count": len(requests),
 		"announcement":               groupAnnouncementPayload(announcement),
-		"permissions":                groupPermissions(selfSub.ModeGiven & selfSub.ModeWant),
+		"permissions":                groupPermissions(access),
 	})
 }