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/lib/tinode/topics.ts

@@ -95,8 +95,8 @@ export function getMessagesSnapshot(topicName: string): StoredMessage[] {
 
 /** Deduped the same way openConversation/connect are -- subscribing the same `me` topic twice
  *  concurrently is the same non-idempotent-WS-call shape as those (currently reachable from
- *  RequireAuth.tsx/LoginPage.tsx/RegisterPage.tsx, which don't overlap today, but this is cheap
- *  insurance against a future call site that does, e.g. a manual "reload contacts" retry button). */
+ *  RequireAuth.tsx/LoginPage.tsx, which don't overlap today, but this is cheap insurance against a
+ *  future call site that does, e.g. a manual "reload contacts" retry button). */
 let inFlightMeSubscribe: Promise<unknown> | null = null;
 
 /** Call once at session start (after login) -- chat-list metadata only, no message bodies. */
@@ -214,6 +214,34 @@ export async function closeConversation(topicName: string): Promise<void> {
   await getTinode().getTopic(topicName).leave(false).catch(() => {});
 }
 
+/**
+ * Makes sure a topic can be published to right now, without disturbing whichever conversation is
+ * actually open. `Topic.publishMessage()` rejects outright unless `_attached` is true, and that's
+ * only reliably the case for the ONE topic openConversation/closeConversation currently has open --
+ * any OTHER topic you've ever actually opened and then navigated away from goes back to detached and
+ * STAYS that way (closeConversation's leave() doesn't restore prefetchPreview's original one-shot
+ * subscription, and prefetchPreview itself no-ops on a topic it's already touched once, attached or
+ * not). That covers forwarding a message to anyone other than the person/group you're currently
+ * chatting with -- i.e. most real forwards -- so this isn't a rare edge case to special-case around,
+ * it's the common one. Reuses `inFlightSubscribe` so a concurrent openConversation() for the same
+ * topic is awaited/shared rather than racing it with a second `{sub}` packet (see openConversation's
+ * own comment above for why that matters). Deliberately left attached afterward rather than re-left --
+ * same "cheap to leave attached, likely reopened soon anyway" call prefetchPreview already makes.
+ */
+export function ensureTopicAttached(topicName: string): Promise<Topic> {
+  const topic = getTinode().getTopic(topicName);
+  const pending = inFlightSubscribe.get(topicName);
+  if (pending) return pending;
+  if (topic.isSubscribed()) return Promise.resolve(topic);
+  wireTopicCallbacks(topic);
+  const promise = topic.subscribe().then(() => topic);
+  inFlightSubscribe.set(topicName, promise);
+  promise.finally(() => {
+    if (inFlightSubscribe.get(topicName) === promise) inFlightSubscribe.delete(topicName);
+  });
+  return promise;
+}
+
 let chatListSnapshot: Contact[] | null = null;
 
 /**