feat(project-editor): add ProjectValidator with MVP validation rules

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/i18n/translations.ts

@@ -502,6 +502,14 @@ export interface Translations {
     importSource: string;
     importError: string;
     featureFlags: string;
+    validationMissingLogo: string;
+    validationNoLanguages: string;
+    validationInvalidUrl: string;
+    validationDuplicateSlugs: string;
+    validationEmptyHomepage: string;
+    validationMissingWidget: string;
+    validationDuplicateNavLinks: string;
+    validationInvalidColors: string;
   };
   staticPages: {
     notFound: string;