fix: 思考对话历史中识别管理员 — 含【管理员】标记的消息标签为'管理员'而非'用户'

之前所有非昔涟的消息都标为[用户]，管理员在群聊中的发言也不例外，
导致模型将管理员误认为普通群友。现在检测内容中的【管理员】前缀。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/ai-core/internal/background/thinker.go

@@ -818,6 +818,36 @@ func (t *Thinker) performThink(triggerReason string) {
 				log.Printf("[后台思考] 频道记忆补充 %d 条", len(memories)-oldCount)
 			}
 		}
+
+		// Also pull recent channel/group memories so the model is aware of group activity.
+		if t.memClient != nil && len(t.platformChannels) > 0 {
+			chanSeen := make(map[string]bool)
+			for _, m := range memories {
+				chanSeen[m.ID] = true
+			}
+			oldCount := len(memories)
+			for _, ch := range t.platformChannels {
+				namespace := fmt.Sprintf("platform_%s_%s_%s", ch.Platform, ch.ChannelType, ch.ChannelID)
+				chanMems, cErr := t.memClient.Query(ctx, model.MemoryQuery{
+					UserID: namespace,
+					Limit:  5,
+				})
+				if cErr != nil {
+					continue
+				}
+				for _, m := range chanMems {
+					if !chanSeen[m.ID] {
+						chanSeen[m.ID] = true
+						labeled := m
+						labeled.Content = fmt.Sprintf("[群聊%s] %s", ch.ChannelID, m.Content)
+						memories = append(memories, labeled)
+					}
+				}
+			}
+			if len(memories) > oldCount {
+				log.Printf("[后台思考] 频道记忆补充 %d 条", len(memories)-oldCount)
+			}
+		}
 	}
 
 	// 4. 查询 IoT 设备状态（每次都查询，无间隔限制）
@@ -1150,6 +1180,8 @@ func (t *Thinker) buildThinkingUserPrompt(
 				roleLabel := "用户"
 				if msg.Role == model.RoleAssistant {
 					roleLabel = "昔涟"
+				} else if strings.Contains(msg.Content, "【管理员】") {
+					roleLabel = "管理员"
 				}
 				content := msg.Content
 				runes := []rune(content)