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/core-bridge/protocol/account.ts

@@ -17,7 +17,7 @@ export interface VaultResource {
   expiresAt: number;
   creatorAccount?: string;
   name?: string;
-  seats: number;
+  maxMembers: number;
   ttlSeconds?: number;
   maxDownloads?: number | null;
   maxVisitors?: number;

web/src/core-bridge/protocol/workspace.ts

@@ -8,7 +8,6 @@ export interface PublishedFile {
   mime: string;
   size: number;
   ts: number;
-  deviceId: string;
   gated: boolean;
 }
 export type ResourceControl = { op: 'file.published'; item: PublishedFile };