Camera rounds: several people's cameras at once in the voice tiles

- A viewer holds one screen and any number of cameras; cameras play in the
  tiles (own one mirrored), a click enlarges one
- "Watch all cameras" joins the round: cameras in the channel are watched as
  they come on. Turning your own camera on joins it too
- Sound, statistics and stop work per stream
- Relay quotas and port range raised: a round uses a route per pair of people

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

src/ui/RightPanel.svelte

@@ -131,7 +131,7 @@
           <Icon name={session.sharing[user.session]} size={16} />
           <span>{isSelf ? `You are sharing your ${session.sharing[user.session]}` : `Sharing their ${session.sharing[user.session]}`}</span>
           {#if isSelf}<button class="btn" onclick={() => share.stop()}>Stop sharing</button>
-          {:else if share.watching?.session === user.session}<button class="btn" onclick={() => share.unwatch()}>Stop watching</button>
+          {:else if share.watchOf(user.session)}<button class="btn" onclick={() => share.unwatch(user.session)}>Stop watching</button>
           {:else}<button class="btn primary" onclick={() => share.watch(sessions.active, user.session)}>Watch</button>{/if}
         </div>
       {/if}