fix(themes): white editor and grey sidebar in light theme

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

frontend/tailwind.config.js

@@ -14,6 +14,8 @@ export default {
     extend: {
       colors: {
         canvas: v('--bg-app'),
+        editor: v('--bg-editor'),
+        sidebar: v('--bg-sidebar'),
         panel: {
           DEFAULT: v('--bg-panel'),
           elevated: v('--bg-panel-elevated'),