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/tests/components/layout/Header.test.tsx

@@ -63,7 +63,7 @@ describe('Header', () => {
 
       render(<Header />);
 
-      expect(screen.getByText('PragmaStack')).toBeInTheDocument();
+      expect(screen.getByText('Syndarix')).toBeInTheDocument();
     });
 
     it('renders theme toggle', () => {