feat(scheduler): add scheduled jobs with channel-aware delivery

Introduce persisted cron/interval jobs, gateway scheduler loop, worker turns,
and admin CRUD/edit UI. Route proactive reminders via the originating chat
channel (WhatsApp vs WeChat), harden Weixin outbound with durable queue and
PG-compatible polling, and fix chat UI to show each scheduled reminder separately.

Co-authored-by: Cursor <cursoragent@cursor.com>

interfaces/admin/static/index.html

@@ -65,6 +65,7 @@
           <div class="nav__group">
             <div class="nav__groupTitle">系统与运行</div>
             <a class="nav__item" data-page="stack" href="#/stack" data-i18n="nav.stack">Runtime</a>
+            <a class="nav__item" data-page="scheduled-jobs" href="#/scheduled-jobs" data-i18n="nav.scheduledJobs">定时任务</a>
             <a class="nav__item" data-page="session-monitor" href="#/session-monitor" data-i18n="nav.sessionMonitor">会话监控</a>
             <a class="nav__item" data-page="workspace-paths" href="#/workspace-paths" data-i18n="nav.workspacePaths">工作区路径</a>
             <a class="nav__item" data-page="attachments" href="#/attachments" data-i18n="nav.attachments">附件</a>