feat: 模块化命令框架 + runbook 严格断言与查询结果回传

- core/module: 命令模板、门控（feature flag/confirm/dry-run）、ecode 错误标签、ResultFormatter
- runbook executor: http.get/http.post/assert.json(expect_success 严格断言)、目标主机管理、任务落库、最终 stdout 直接回传
- cf 模块: /cf dns list 支持域名自动解析 zone_id；dns list/zones/workers list 格式化回传；API success:false 判真失败
- 全部 CF/CPA runbook 接入严格断言，杜绝假阳性 success
- 新增 cpa/cfdav/mail/sub 模块与 runbooks；QQ 订阅到期提醒调度
- Web 后台: 模块设置(CF/CPA/cfdav/AI)、OPS 任务、渠道管理、审计页

internal/core/policy/policy.go

@@ -0,0 +1,62 @@
+package policy
+
+import (
+	"errors"
+	"strings"
+
+	"gorm.io/gorm"
+
+	"ops-assistant/models"
+)
+
+type GateRequest struct {
+	NeedFlag       string
+	RequireConfirm bool
+	ConfirmToken   string
+	ExpectedToken  string
+	AllowDryRun    bool
+	DryRun         bool
+}
+
+func ParseCommonFlags(text string) (dryRun bool, confirmToken string) {
+	parts := strings.Fields(strings.TrimSpace(text))
+	for i := 0; i < len(parts); i++ {
+		if parts[i] == "--dry-run" {
+			dryRun = true
+		}
+		if parts[i] == "--confirm" && i+1 < len(parts) {
+			confirmToken = strings.TrimSpace(parts[i+1])
+			i++
+		}
+	}
+	return
+}
+
+func FlagEnabled(db *gorm.DB, key string) bool {
+	if strings.TrimSpace(key) == "" {
+		return true
+	}
+	var ff models.FeatureFlag
+	if err := db.Where("key = ?", key).First(&ff).Error; err != nil {
+		return false
+	}
+	return ff.Enabled
+}
+
+func CheckGate(db *gorm.DB, req GateRequest) error {
+	if strings.TrimSpace(req.NeedFlag) != "" && !FlagEnabled(db, req.NeedFlag) {
+		return errors.New("feature flag 未启用: " + req.NeedFlag)
+	}
+	if req.RequireConfirm {
+		if strings.TrimSpace(req.ConfirmToken) == "" {
+			return errors.New("缺少 --confirm <token>")
+		}
+		if strings.TrimSpace(req.ExpectedToken) != "" && strings.TrimSpace(req.ConfirmToken) != strings.TrimSpace(req.ExpectedToken) {
+			return errors.New("确认 token 无效")
+		}
+	}
+	if req.DryRun && !req.AllowDryRun {
+		return errors.New("当前命令不允许 dry-run")
+	}
+	return nil
+}