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/channel/LatestCard.tsx

@@ -1,7 +1,8 @@
 import { formatSize, formatTime, formatTransferProgress } from '@/lib/format';
 import { useDownload } from '@/features/item/download';
 import { InlineContent, inlineKindOf } from '@/features/item/InlineContent';
-import { shortDevice, titleOf } from '@/features/item/summary';
+import { senderLabel } from '@/lib/sender';
+import { titleOf } from '@/features/item/summary';
 import { Tile } from '@/features/item/Tile';
 import { useWorkspace } from '@/store/workspace';
 import { Button } from '@/ui/Button';
@@ -16,7 +17,6 @@ interface Props {
 /** 手机首屏:最新一项放大,拇指区一键取走 */
 export function LatestCard({ id, onOpen }: Props) {
   const item = useWorkspace((s) => s.byId[id]);
-  const device = useWorkspace((s) => s.devices.find((d) => d.id === s.byId[id]?.deviceId)?.name);
   const download = useDownload();
   if (!item) return null;
 
@@ -32,7 +32,7 @@ export function LatestCard({ id, onOpen }: Props) {
         <span className={styles.text}>
           {inline === 'text' ? null : <span className={styles.title}>{titleOf(item)}</span>}
           <span className={styles.sub}>
-            {shortDevice(device)} · {formatTime(item.ts)} · {formatSize(size)}
+            {senderLabel(item)} · {formatTime(item.ts)} · {formatSize(size)}
             {receiving !== null && item.state.kind === 'receiving' ? ` · ${formatTransferProgress(item.state)}` : ''}
           </span>
         </span>