feat: complete Syndarix rebranding from PragmaStack

- Update PROJECT_NAME to Syndarix in backend config
- Update all frontend components with Syndarix branding
- Replace all GitHub URLs with Gitea Syndarix repo URLs
- Update metadata, headers, footers with new branding
- Update tests to match new URLs
- Update E2E tests for new repo references
- Preserve "Built on PragmaStack" attribution in docs

Closes #13

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/app/[locale]/demos/page.tsx

@@ -26,8 +26,8 @@ import { Badge } from '@/components/ui/badge';
 import { Separator } from '@/components/ui/separator';
 
 export const metadata: Metadata = {
-  title: 'Demo Tour | PragmaStack',
-  description: 'Try all features with demo credentials - comprehensive guide to the PragmaStack',
+  title: 'Demo Tour | Syndarix',
+  description: 'Try all features with demo credentials - comprehensive guide to the Syndarix',
 };
 
 const demoCategories = [