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/App.svelte

@@ -60,7 +60,7 @@
     {#if layout === 'narrow'}<button class="scrim" aria-label="Close" onclick={() => (navOpen = false)}></button>{/if}
   {/if}
 
-  <Chat showMenu={layout === 'narrow'} onmenu={() => (navOpen = true)} onpanel={togglePanel} />
+  <Chat showMenu={layout === 'narrow'} showStage={layout !== 'wide'} onmenu={() => (navOpen = true)} onpanel={togglePanel} />
 
   {#if showPanel}
     {#if layout === 'wide'}