feat(ui): Discord-style roles/channel perms + IDE themes

Split-pane role editor with tri-state channel overrides (roles/members).
CSS-var themes (Gruvbox default + 9 IDE palettes) in top bar and settings.

web/src/components/Layout.tsx

@@ -14,6 +14,7 @@ import { NotificationPrompt } from './NotificationPrompt.tsx';
 import { MemberList } from './MemberList.tsx';
 import { VoicePanel } from './VoicePanel.tsx';
 import { ServerSettingsModal } from './ServerSettingsModal.tsx';
+import { ThemeToggle } from './ThemeToggle.tsx';
 
 const STATUS_CYCLE: UserStatus[] = ['online', 'idle', 'dnd', 'offline'];
 function statusColor(status: UserStatus): string {
@@ -134,6 +135,9 @@ export function Layout() {
                 </div>
               )}
             </div>
+            <div className="hidden sm:block">
+              <ThemeToggle />
+            </div>
             <Link to="/settings" className="terminal-button text-xs px-1.5 py-0.5 hidden sm:inline-flex">[SETTINGS]</Link>
             {activeServerId && (
               <button onClick={() => setShowServerSettings(true)}