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/UserSettings.tsx

@@ -2,6 +2,7 @@ import { useState, useRef, useEffect } from 'react';
 import { Link, useNavigate } from 'react-router-dom';
 import { useAuthStore } from '../stores/auth.ts';
 import { usePushStore } from '../stores/push.ts';
+import { ThemeToggle } from './ThemeToggle.tsx';
 
 export function UserSettings() {
   const { user, updateProfile, changePassword, isLoading, error, clearError } = useAuthStore();
@@ -316,6 +317,17 @@ export function UserSettings() {
               </div>
             </div>
 
+            {/* Appearance */}
+            <div className="border border-gb-bg-t p-4">
+              <label className="block text-gb-fg-f mb-2 font-mono text-sm">
+                THEME:
+              </label>
+              <ThemeToggle />
+              <p className="text-gb-fg-f text-xs font-mono mt-2">
+                Default is Gruvbox. Choice is saved in this browser.
+              </p>
+            </div>
+
             {/* Push Notifications */}
             {isSupported && (
               <div className="border border-gb-bg-t p-4">