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/ConnectDialog.svelte

@@ -5,14 +5,18 @@
   import { identities } from '../lib/identities.svelte.ts';
   import { makeServerIcon } from '../lib/upload.ts';
 
-  let { server, onclose }: { server: SavedServer | null; onclose: () => void } = $props();
+  // prefill: values for a new server, e.g. picked from the public list
+  let { server, prefill, onclose }: { server: SavedServer | null; prefill?: { host?: string; port?: number; label?: string }; onclose: () => void } = $props();
 
   // svelte-ignore state_referenced_locally
   const initial = server;
-  let label = $state(initial?.label ?? '');
-  let host = $state(initial?.host ?? '');
-  let port = $state(initial?.port ?? 64738);
-  let username = $state(initial?.username ?? '');
+  // svelte-ignore state_referenced_locally
+  const pre = prefill ?? {};
+  let label = $state(initial?.label ?? pre.label ?? '');
+  let host = $state(initial?.host ?? pre.host ?? '');
+  let port = $state(initial?.port ?? pre.port ?? 64738);
+  // New servers start with the name you used last
+  let username = $state(initial?.username ?? store.servers.at(-1)?.username ?? '');
   let password = $state(initial?.password ?? '');
   let identityId = $state(initial?.identityId ?? '');
   let icon = $state(initial?.icon ?? '');