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/Message.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
   import Avatar from './Avatar.svelte';
   import YouTubeEmbed from './YouTubeEmbed.svelte';
+  import LinkPreview from './LinkPreview.svelte';
   import { store } from '../lib/settings.svelte.ts';
   import type { ChatEntry } from '../lib/session.svelte.ts';
 
@@ -33,7 +34,9 @@
       {/if}
       {#if entry.html}<div class="html">{@html entry.html}</div>{/if}
       {#each entry.embeds as m (m.url)}
-        {#if m.kind === 'youtube'}
+        {#if m.kind === 'link'}
+          <div class="embed"><LinkPreview url={m.url} /></div>
+        {:else if m.kind === 'youtube'}
           {#if store.settings.youtube !== 'off'}<div class="embed"><YouTubeEmbed videoId={m.videoId!} start={m.start} url={m.url} /></div>{/if}
         {:else}
         <div class="embed">