fix(projects): fix breadcrumb showing i18n key instead of translated text (#931)

Fixes #929. The breadcrumb in ProjectDetailPage used the non-existent key
`navigation.projects`. Changed to the correct key `nav.projects` which is
defined in all locale files and resolves to e.g. 'Projects' in English.

frontend/src/pages/ProjectDetailPage.tsx

@@ -456,7 +456,7 @@ export function ProjectDetailPage() {
       {/* Breadcrumb */}
       <div className="flex items-center gap-2 text-sm text-bambu-gray">
         <Link to="/projects" className="hover:text-white transition-colors">
-          {t('navigation.projects')}
+          {t('nav.projects')}
         </Link>
         <ChevronRight className="w-4 h-4" />
         <span className="text-white">{project.name}</span>