Add channel and permission management, sounds, themes and the public server list

- Channels: create, edit, delete, link and move (drag and drop for channels and
  people), right-click on free space in the channel list
- Permission editor with inherited rules, allow/deny per permission, groups and
  members; menus grey out actions the server does not allow
- Notification sounds for connection, channel, chat, mute and push-to-talk events;
  custom files and TeamSpeak 3 style sound packs (settings.ini), stored in IndexedDB
- Color schemes: Dark, Light, Midnight, Frost and Windows 95
- Public server list with live UDP ping, fetched through Chromium's network stack
- Kick, ban and connection-lost card with Reconnect
- Right-click menus for text fields, links, images and message authors
- Formatting toolbar in the message box, shared with the description editor
- Resizable channel list, menu headers, registration from the self menu only
- Fix: client-side pacing now mirrors Murmur's whole-second leaky bucket exactly,
  so quick actions are no longer dropped silently

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

src/ui/ServerRail.svelte

@@ -5,8 +5,8 @@
   import { menu } from '../lib/menu.svelte.ts';
   import { makeServerIcon } from '../lib/upload.ts';
 
-  let { onadd, onedit, onsettings }:
-    { onadd: () => void; onedit: (s: SavedServer) => void; onsettings: () => void } = $props();
+  let { onadd, onedit, onsettings, onbrowse }:
+    { onadd: () => void; onedit: (s: SavedServer) => void; onsettings: () => void; onbrowse: () => void } = $props();
 
   const initials = (label: string) =>
     label.split(/[\s._-]+/).filter(Boolean).slice(0, 2).map(w => w[0]).join('').toUpperCase() || '?';
@@ -50,6 +50,7 @@
   function serverMenu(e: MouseEvent, s: SavedServer, i: number) {
     const state = stateOf(s.id);
     menu.show(e, [
+      { header: true, label: s.label },
       state === 'idle'
         ? { label: 'Connect', action: () => sessions.open(s) }
         : { label: 'Disconnect', action: () => sessions.close(s.id) },
@@ -87,6 +88,7 @@
   {#if dropIndex === store.servers.length && dragging}<div class="drop-line"></div>{/if}
   <input bind:this={iconPicker} type="file" accept="image/*" hidden onchange={pickIcon} />
   <button class="tile add" title="Add a server" onclick={onadd}><Icon name="plus" /></button>
+  <button class="tile add" title="Browse public servers" onclick={onbrowse}><Icon name="globe" /></button>
   <div class="spacer"></div>
   <button class="tile ghost" title="Settings" onclick={onsettings}><Icon name="settings" /></button>
 </nav>