feat: 主动消息写回对话历史 — 防止短期重复提问

- storeThought 推送主动消息后写入 convStore
- 轻量思考话题发起后也写入
- 配合提示词规则: 两小时内不重复问同类话题

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

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

@@ -929,6 +929,9 @@ func (t *Thinker) performLightThink() {
 			t.mu.Unlock()
 			if pusher != nil && canPush {
 				go pusher(t.adminUserID, sessionID, topic)
+				if t.convStore != nil && sessionID != "" {
+					t.convStore.AddMessage(sessionID, model.LLMMessage{Role: model.RoleAssistant, Content: topic})
+				}
 			}
 		}
 	}
@@ -1873,9 +1876,15 @@ func (t *Thinker) storeThought(content string, toolCallsJSON string, toolCallCou
 				log.Printf("[后台思考] 推送平台主动消息: target=%s/%s user=%s group=%s msg=%s",
 					targetCopy.Platform, targetCopy.ChatType, targetCopy.UserID, targetCopy.GroupID, proactiveMsg)
 				platformPusher(*targetCopy, proactiveMsg)
+				if t.convStore != nil && pushSessionID != "" {
+					t.convStore.AddMessage(pushSessionID, model.LLMMessage{Role: model.RoleAssistant, Content: proactiveMsg})
+				}
 			} else {
-				log.Printf("[后台思考] 推送主动消息: %s", proactiveMsg)
+				log.Printf("[后台思考] 推送主动消息: %%s", proactiveMsg)
 				pusher(t.adminUserID, pushSessionID, proactiveMsg)
+				if t.convStore != nil && pushSessionID != "" {
+					t.convStore.AddMessage(pushSessionID, model.LLMMessage{Role: model.RoleAssistant, Content: proactiveMsg})
+				}
 			}
 		}()
 	}