fix(i18n): route dirty-guard and html-editor strings through TranslateService

window.confirm/window.prompt calls in projectEditorDirtyGuard and
MarketplaceHtmlEditorComponent, and the hardcoded Preview/Code toggle
label in its template, bypassed the app's translation pipeline. Add
builder.confirmLeaveUnsaved, promptLinkUrl, promptImageUrl,
htmlEditorCode and htmlEditorPreview keys (en/ru/hy), resolve them via
TranslateService.t() before passing to confirm/prompt, and use
TranslatePipe for the toggle button label.

src/app/i18n/en.ts

@@ -517,6 +517,11 @@ export const en: Translations = {
     unsavedChanges: 'Unsaved changes',
     save: 'Save',
     publish: 'Publish',
+    confirmLeaveUnsaved: 'You have unsaved changes. Leave anyway?',
+    promptLinkUrl: 'URL',
+    promptImageUrl: 'Image URL',
+    htmlEditorCode: 'Code',
+    htmlEditorPreview: 'Preview',
   },
   staticPages: {
     notFound: 'Page not found',