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/registry/registry.go

@@ -0,0 +1,47 @@
+package registry
+
+import (
+	"sort"
+
+	"ops-assistant/internal/core/command"
+)
+
+type Handler func(userID int64, cmd *command.ParsedCommand) (string, error)
+
+type Registry struct {
+	handlers       map[string]Handler
+	moduleHandlers map[string]Handler
+}
+
+func New() *Registry {
+	return &Registry{handlers: map[string]Handler{}, moduleHandlers: map[string]Handler{}}
+}
+
+func (r *Registry) Register(name string, h Handler) {
+	r.handlers[name] = h
+}
+
+func (r *Registry) RegisterModule(module string, h Handler) {
+	r.moduleHandlers[module] = h
+}
+
+func (r *Registry) Handle(userID int64, cmd *command.ParsedCommand) (string, bool, error) {
+	if h, ok := r.handlers[cmd.Name]; ok {
+		out, err := h(userID, cmd)
+		return out, true, err
+	}
+	if h, ok := r.moduleHandlers[cmd.Module]; ok {
+		out, err := h(userID, cmd)
+		return out, true, err
+	}
+	return "", false, nil
+}
+
+func (r *Registry) ListModules() []string {
+	mods := make([]string, 0, len(r.moduleHandlers))
+	for m := range r.moduleHandlers {
+		mods = append(mods, m)
+	}
+	sort.Strings(mods)
+	return mods
+}