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

frontend/src/app/globals.css

@@ -1,7 +1,7 @@
 @import 'tailwindcss';
 
 /**
- * PragmaStack Design System
+ * Syndarix Design System
  * Theme: Modern Minimal (from tweakcn.com)
  * Primary: Blue | Color Space: OKLCH
  *