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/features/home/ChannelList.tsx

@@ -46,7 +46,7 @@ export function ChannelList({ kind, title, onOpen }: Props) {
                       {c.mode === 'enc' ? <><Icon name="lock" size={12} /> 加密</> : '明文'}
                     </span>
                     <span>{c.role === 'owner' ? '所有者' : '成员'}</span>
-                    <span>最多 {c.seats} 人</span>
+                    <span>最多 {c.maxMembers} 人</span>
                     <span>{formatAgo(c.createdAt)}创建</span>
                   </>
                 )}