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

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

frontend/tests/lib/i18n/metadata.test.ts

@@ -27,8 +27,8 @@ describe('metadata utilities', () => {
     });
 
     it('should have English and Italian names', () => {
-      expect(siteConfig.name.en).toBe('PragmaStack');
-      expect(siteConfig.name.it).toBe('PragmaStack');
+      expect(siteConfig.name.en).toBe('Syndarix');
+      expect(siteConfig.name.it).toBe('Syndarix');
     });
 
     it('should have English and Italian descriptions', () => {