Add client feature to ensure full backwards compatibility with themes

packages/builder/src/pages/builder/app/[application]/design/[screenId]/_components/AppPreview.svelte

@@ -19,7 +19,7 @@
   import { findComponent, findComponentPath } from "helpers/components"
   import { isActive, goto } from "@roxi/routify"
   import { ClientAppSkeleton } from "@budibase/frontend-core"
-  import { getThemeClassNames } from "@budibase/shared-core"
+  import { getThemeClassNames, ThemeClassPrefix } from "@budibase/shared-core"
 
   let iframe
   let layout
@@ -48,7 +48,9 @@
     layout,
     screen,
     selectedComponentId,
-    theme: $themeStore.theme,
+    theme: $appStore.clientFeatures.unifiedThemes
+      ? $themeStore.theme
+      : `${ThemeClassPrefix}${$themeStore.theme}`,
     customTheme: $themeStore.customTheme,
     previewDevice: $previewStore.previewDevice,
     messagePassing: $appStore.clientFeatures.messagePassing,

packages/client/manifest.json

@@ -1,6 +1,7 @@
 {
   "features": {
     "spectrumThemes": true,
+    "unifiedTheme": true,
     "intelligentLoading": true,
     "deviceAwareness": true,
     "state": true,