Add server information, an always-visible mute bar and public list actions

- Public servers: connect arrow and add button per row, sortable column headers
- Mute and deafen stay available while disconnected; the choice carries to the next connect
- Server information dialog, opened from a button next to mute
- Stacked layout: mute bar on top, without the profile
- Settings that need the upload host are disabled until it is set; link previews show the mode in effect
- YouTube links are plain links by default
- Composer has a border and matches the sidebar bar height
- Regenerate README screenshots

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

src/lib/ui.svelte.ts

@@ -27,6 +27,7 @@ class Ui {
   quickAudio = $state<{ kind: 'input' | 'output'; x: number; y: number } | null>(null);
   settingsTab = $state<'voice' | 'sounds' | 'appearance' | 'files' | 'identities'>('voice');
   publicServers = $state(false);
+  serverInfo = $state(false);
   // Add-server dialog, optionally prefilled (from the public list)
   addServer = $state<{ host?: string; port?: number; label?: string } | null>(null);
   // Channel dialog: create a subchannel of `parent`, or edit channel `id`