feat(ai): 助手浮窗聚焦日志查询页,携带当前查询结果对话

- 浮球只在 /logs 渲染(产品定位:辅助分析正在查看的查询结果,其它页面不打扰)
- /logs 查询成功后写入 AI 上下文:LogQL、时间范围、结果条数、error 行数、
  最新 20 条样本(去 CRI 包装);对话请求自动携带
- 后端 /ai/chat 接收 context:截断 6000 字 + RedactTextOnly 统一脱敏后并入 system
  (ECHO 假模型实测注入完整);空态文案改为查询导向

backend/controllers/ai.go

@@ -161,6 +161,7 @@ func (ctrl *AIController) Chat(c *gin.Context) {
 		History      []services.ChatMessage `json:"history" binding:"required,min=1,max=40"`
 		Page         string                 `json:"page"`
 		RangeMinutes int                    `json:"rangeMinutes"`
+		Context      string                 `json:"context"`
 	}
 	if !utils.BindAndValidate(c, &req) {
 		return
@@ -174,7 +175,7 @@ func (ctrl *AIController) Chat(c *gin.Context) {
 	if rangeMinutes <= 0 || rangeMinutes > 120 {
 		rangeMinutes = 15
 	}
-	reply, err := services.RunAIChat(c.Request.Context(), cfg, src, c.GetUint("userId"), c.GetString("role") == "admin", req.History, req.Page, rangeMinutes)
+	reply, err := services.RunAIChat(c.Request.Context(), cfg, src, c.GetUint("userId"), c.GetString("role") == "admin", req.History, req.Page, rangeMinutes, req.Context)
 	if err != nil {
 		utils.Error(c, 400, err.Error())
 		return