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/preload.ts

@@ -12,6 +12,7 @@ for (const key of Object.keys(listeners) as (keyof typeof listeners)[]) {
 contextBridge.exposeInMainWorld('mumh5Native', {
   platformInfo: () => ipcRenderer.invoke('platform:info'),
   updateTray: (state: unknown) => ipcRenderer.send('tray:update', state),
+  linkPreview: (url: string) => ipcRenderer.invoke('preview:fetch', url),
   onTrayAction: (fn: (action: string) => void) => { ipcRenderer.on('tray:action', (_e, a: string) => fn(a)); },
   describeCerts: (ders: Uint8Array[]) => ipcRenderer.invoke('certs:describe', ders),
   identities: {