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/AccountDevices.tsx

@@ -26,7 +26,7 @@ export function AccountDevices() {
     <div className={styles.sectionHeader}><strong>我的设备</strong>
       <Button variant="ghost" disabled={busy} onClick={() => { void refresh().catch(() => setError('设备清单读取失败')); }}>刷新设备</Button>
     </div>
-    <p className={styles.note}>同一账号可登录多台设备。移除设备会撤销它的登录与空间席位，保留账号的空间成员资格。</p>
+    <p className={styles.note}>同一账号可登录多台设备。移除设备只会撤销它的登录，不影响账号在各空间里的成员身份。</p>
     {devices.map((device) => <div className={styles.deviceRow} key={device.id}>
       <label className={styles.deviceName}>
         <input aria-label={`${device.name} 的设备名称`} maxLength={80} value={names[device.id] ?? device.name} onChange={(e) => setNames((values) => ({ ...values, [device.id]: e.target.value }))} />