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>

src/ui/ChannelNode.svelte

@@ -48,7 +48,7 @@
       <span class="caret"></span>
     {/if}
     <button class="name" title="Click for details, double-click to join" {...channelClicks}>
-      <Icon name={channel.canEnter ? 'channel' : 'lock'} size={16} />
+      {#if !channel.canEnter}<Icon name="lock" size={14} />{/if}
       <span class="label">{channel.name || 'Root'}</span>
       {#if !expanded && total > 0}<span class="count" title="{total} {total === 1 ? 'person' : 'people'} inside">{total}</span>{/if}
       {#if unread}<span class="badge">{unread}</span>{/if}