Add link previews, voice tiles and a menu volume slider; tidy the profile

- Link previews for web links in chat, fetched by the f0ckm upload host by
  default (linked sites never see the user's IP), or directly, or off
- Voice channel tiles above the chat on windows too narrow for the member list
- Per-person volume slider in the user context menu
- Profile panel: channel on its own line under the name, no Guest badge,
  voice actions moved to the context menu
- User information dialog refreshes every second
- Rate limiting mirrors Murmur's whole-second bucket leak, so irregular
  bursts are queued instead of dropped
- CHANGELOG.md

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

electron/main.ts

@@ -5,6 +5,7 @@ import path from 'node:path';
 import { IdentityStore } from './identity-store.ts';
 import { describeCert } from './certs.ts';
 import * as tray from './tray.ts';
+import { fetchLinkPreview } from './link-preview.ts';
 import { openTls } from './tls-transport.ts';
 
 const devUrl = process.env.VITE_DEV_SERVER_URL;
@@ -74,6 +75,8 @@ ipcMain.on('mumble:close', (e, connId: string) => {
 ipcMain.handle('certs:describe', (_e, ders: Uint8Array[]) =>
   (Array.isArray(ders) ? ders.slice(0, 8) : []).flatMap(d => { try { return [describeCert(Buffer.from(d))]; } catch { return []; } }));
 
+ipcMain.handle('preview:fetch', (_e, url: string) => fetchLinkPreview(String(url).slice(0, 2048)));
+
 ipcMain.on('tray:update', (_e, state: tray.TrayState) => tray.update(state));
 
 ipcMain.handle('platform:info', () => ({ os: process.platform, osVersion: os.release() }));