实现 P0 自动分配、离线留言与可嵌入 Widget SDK

- 会话创建时按负载自动分配在线客服，无客服则进入离线模式
- 新增 /api/widget/leave-message 沉淀联系方式与留言事件
- 访客端离线留言表单；工作台展示离线留言/自动分配事件
- 提供 public/widget.js + /widget/embed 嵌入方案

web/src/pages/agent/Dashboard.tsx

@@ -253,7 +253,7 @@ const Dashboard = () => {
       return tb - ta
     })
 
-  const notes = detail?.events.filter(event => event.action === 'note').slice().reverse() || []
+  const notes = detail?.events.filter(event => event.action === 'note' || event.action === 'offline_leave' || event.action === 'auto_assign').slice().reverse() || []
 
   const emitTyping = () => {
     if (!selectedId || !canOperate) return
@@ -899,12 +899,25 @@ const Dashboard = () => {
                 <div className="space-y-2 max-h-40 overflow-auto">
                   {notes.length === 0 ? (
                     <div className="text-xs text-neutral-400">暂无内部备注</div>
-                  ) : notes.map(note => (
-                    <div key={note.id} className="bg-amber-50 text-amber-900 rounded-lg p-2 text-xs whitespace-pre-wrap border border-amber-100">
-                      {note.detail}
-                      <div className="text-amber-600/70 mt-1">{new Date(note.created_at).toLocaleString('zh-CN')}</div>
-                    </div>
-                  ))}
+                  ) : notes.map(note => {
+                    const isLeave = note.action === 'offline_leave'
+                    const isAssign = note.action === 'auto_assign'
+                    const box = isLeave
+                      ? 'bg-orange-50 text-orange-900 border-orange-100'
+                      : isAssign
+                        ? 'bg-blue-50 text-blue-900 border-blue-100'
+                        : 'bg-amber-50 text-amber-900 border-amber-100'
+                    const timeCls = isLeave ? 'text-orange-600/70' : isAssign ? 'text-blue-600/70' : 'text-amber-600/70'
+                    return (
+                      <div key={note.id} className={`rounded-lg p-2 text-xs whitespace-pre-wrap border ${box}`}>
+                        {(isLeave || isAssign) && (
+                          <div className="font-medium mb-0.5">{isLeave ? '离线留言' : '自动分配'}</div>
+                        )}
+                        {note.detail}
+                        <div className={`mt-1 ${timeCls}`}>{new Date(note.created_at).toLocaleString('zh-CN')}</div>
+                      </div>
+                    )
+                  })}
                 </div>
                 {canOperate && (
                   <div className="mt-2 flex gap-1">