feat(web): discord-style chat, members pane, invitations and optimistic send [CI]

- chat: left-aligned discord-style messages with grouped senders, hover
  actions, an auto-growing composer and file cards
- send: render messages and files locally first and replace the
  placeholder when the worker publishes the real item; failures keep the
  text with a retry action
- navigation: space rail plus a flatter channel list with the space name
  header and collapsible groups
- members: right pane tabs (files / members) grouped by online, offline
  and pending users, with a prominent invite action and a top bar shortcut
- notifications: toast host for invite results; invitees get a toast with
  an accept action, and the invitation payload now carries the space name
  and inviter inside the encrypted grant
- users over devices: drop device names, the device list and device
  rename/release; senders show the account (guests show as guest) and the
  share panel only keeps links
- follow contract 7.0.0 (max_members, members_used, members_full, /join)
- docs: ui-design and frontend updated for the new layout and concepts

web/src/app/useInvitationNotices.ts

@@ -0,0 +1,48 @@
+import { useEffect, useRef } from 'react';
+import { accountApi, type AccountInvitation } from '@/core-bridge/account';
+import { errorMessage } from '@/core-bridge/errors';
+import { useChannels } from '@/store/channels';
+import { useToast } from '@/store/toast';
+import { channelPath, navigate } from './navigation';
+
+const POLL_MS = 8000;
+
+export function invitationLabel(row: AccountInvitation): string {
+  return row.channelName || `空间 ${row.channel_id.slice(0, 8)}…`;
+}
+
+async function accept(row: AccountInvitation): Promise<void> {
+  try {
+    await accountApi.acceptInvitation(row.channel_id);
+    await useChannels.getState().refresh();
+    useToast.getState().push({ kind: 'ok', text: `已加入 ${invitationLabel(row)}` });
+    navigate(channelPath(row.channel_id));
+  } catch (cause) {
+    useToast.getState().push({ kind: 'error', text: `加入失败：${errorMessage(cause)}` });
+  }
+}
+
+/** 登录后轮询账号邀请,出现新邀请就弹通知,可直接接受 */
+export function useInvitationNotices(username: string | null): void {
+  const seen = useRef<Set<string> | null>(null);
+  useEffect(() => {
+    if (!username) { seen.current = null; return; }
+    let stopped = false;
+    async function poll() {
+      try {
+        const rows = await accountApi.invitations();
+        if (stopped) return;
+        const known = seen.current;
+        seen.current = new Set(rows.map((row) => row.channel_id));
+        const fresh = known ? rows.filter((row) => !known.has(row.channel_id)) : rows;
+        for (const row of fresh) {
+          useToast.getState().push({ kind: 'info', text: row.invitedBy ? `${row.invitedBy} 邀请你加入 ${invitationLabel(row)}` : `你收到了加入 ${invitationLabel(row)} 的邀请`,
+            action: { label: '接受', run: () => { void accept(row); } } });
+        }
+      } catch { /* 下一轮再试,不打扰用户 */ }
+    }
+    void poll();
+    const timer = window.setInterval(() => { void poll(); }, POLL_MS);
+    return () => { stopped = true; window.clearInterval(timer); };
+  }, [username]);
+}