feat(license): 首次安装 14 天 Pro 试用(无需授权码)

- 首次启动落试用起点(DATA_DIR/.trial-start 0600 + 库内 settings 双写,取最早防分次续命);
  窗口内 IsPro() 等效 Pro——日志分析/告警/AI 助手/审计全解锁,到期自动回免费版
- 防刷三层:时间戳双写(删任一不重发)+ 机器级指纹(machine-id / hostname+cpu,
  故意不含 DATA_DIR 特征——目录特征会因删除重建漂移等于后门);指纹命中则落已过期起点
- LicenseStatusPayload 返回 trial{active,daysLeft} 与 plan=trial;
  设置页授权区显示「Pro 试用中 · 剩余 N 天」提示条
- 单测:全新安装 14 天/到期回落/删时间戳重装不重发(指纹防刷)三用例
- 滥用评估:删库重装同机器被指纹拦截;换机器/VM 必然可重试(接受,Pro 功能零边际成本,
  追杀到硬件级得不偿失);正式授权随时激活覆盖试用

backend/services/license.go

@@ -386,8 +386,20 @@ func LicenseStatusPayload() (map[string]interface{}, bool) {
 	current := CurrentLicense()
 	stored := StoredLicense()
 	instanceID := GetOrCreateInstanceID()
+	EnsureTrialStarted()
+	trialDaysLeft := 0
+	if TrialActive() {
+		trialDaysLeft = TrialRemainingDays()
+	}
 	if stored == nil {
-		return map[string]interface{}{"plan": "free", "instanceId": instanceID}, false
+		plan := "free"
+		if trialDaysLeft > 0 {
+			plan = "trial"
+		}
+		return map[string]interface{}{
+			"plan": plan, "instanceId": instanceID,
+			"trial": map[string]interface{}{"active": trialDaysLeft > 0, "daysLeft": trialDaysLeft},
+		}, trialDaysLeft > 0
 	}
 	out := stored.Sanitized()
 	out["instanceId"] = instanceID
@@ -400,7 +412,11 @@ func LicenseStatusPayload() (map[string]interface{}, bool) {
 		out["invalidReason"] = reason
 	}
 	out["plan"] = "free"
-	return out, false
+	if trialDaysLeft > 0 {
+		out["plan"] = "trial"
+	}
+	out["trial"] = map[string]interface{}{"active": trialDaysLeft > 0, "daysLeft": trialDaysLeft}
+	return out, trialDaysLeft > 0
 }
 
 // CurrentLicense 当前有效许可(nil = 免费版)
@@ -444,8 +460,13 @@ func CurrentLicense() *models.License {
 	return lic
 }
 
-// IsPro 是否为有效 Pro
-func IsPro() bool { return CurrentLicense() != nil }
+// IsPro 是否为有效 Pro:正式授权优先;无授权时 14 天试用窗口内等效 Pro
+func IsPro() bool {
+	if CurrentLicense() != nil {
+		return true
+	}
+	return TrialActive()
+}
 
 // ProFeatureList Pro 功能标识(给前端展示)
 func ProFeatureList() []string { return proFeatures }