feat(web): 下线自主注册与协议勾选，修复转发消息报错，转发选择器分组+全选

按产品决定移除面向国内客户不适用的自主注册入口：删除 /register 路由
及 RegisterPage、登录页"马上注册"链接、登录/注册共用的协议勾选组件
Agreement，以及仅注册流程使用的 registerAccount/queueAccExtra 等
死代码；登录不再依赖勾选协议才能提交。

修复转发消息报错（真实高频bug，不限于个别场景）：`forwardMessage`/
`sendText` 发送前只是 `tinode.getTopic()` 取一个本地话题对象，从未
真正订阅——SDK 要求话题处于 attached 状态才允许发布，而只有当前正
打开的会话才满足这一点，一旦切换过/离开过某个会话（哪怕之前订阅过
预览），它就会变回未订阅状态。也就是说转发给"当前会话之外"几乎任何
一个联系人都会失败。新增 `ensureTopicAttached()`，在转发前按需临时
订阅目标话题，单条转发和多选批量转发两处都已接入，实机验证对未打开
过的好友/群转发均成功。

转发选择器（ForwardPickerModal）按好友/群聊分组显示（原来混在一个
列表里），并加了"全选/取消全选"，避免多个接收方时逐条点选。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/app/RequireAuth.tsx

@@ -70,11 +70,11 @@ export function RequireAuth() {
   }, [tenant, myUserId, hasToken, setMyUserId, clearTenant]);
 
   // Single place that ensures the `me` topic gets subscribed once `myUserId` is known, regardless
-  // of HOW it became known (session restore above, or a fresh login/register that already called
-  // setMyUserId before this component ever mounted) -- LoginPage/RegisterPage used to each fire
-  // their own subscribeMeTopic() with a swallowed .catch(() => {}), silently leaving a freshly
-  // logged-in user with an empty conversation list and no error on a transient failure. Centralizing
-  // here means it happens exactly once per authenticated mount and surfaces the same Toast either way.
+  // of HOW it became known (session restore above, or a fresh login that already called
+  // setMyUserId before this component ever mounted) -- LoginPage used to fire its own
+  // subscribeMeTopic() with a swallowed .catch(() => {}), silently leaving a freshly logged-in user
+  // with an empty conversation list and no error on a transient failure. Centralizing here means it
+  // happens exactly once per authenticated mount and surfaces the same Toast either way.
   useEffect(() => {
     if (!myUserId || meSubscribedRef.current) return;
     meSubscribedRef.current = true;