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/lib/sender.ts

@@ -0,0 +1,8 @@
+import type { SenderInfo } from '@/core-bridge/types';
+
+/** 没有账号归属的内容(未登录访客)的显示名;设备只是账号的属性,不作为发送者展示 */
+export const GUEST_LABEL = '访客';
+
+export function senderLabel(source: { author?: SenderInfo } | undefined, fallback = GUEST_LABEL): string {
+  return source?.author?.displayName || source?.author?.username || fallback;
+}