refactor(e2e): use bundled hacdias/webdav instead of mock server

- Replace custom mock server with real hacdias/webdav:latest
- Use existing webdav.yaml configuration and alice/bob users
- Remove unnecessary mock server code following KISS principle
- WebDAV server now matches production setup exactly
- Persistent data storage in ./e2e-webdav-data

This provides more realistic e2e testing with the actual WebDAV
server used in production deployments.

debug-headers.spec.ts

@@ -43,4 +43,4 @@ describe('Debug Headers', () => {
     expect(result).toBe('v1');
     expect(mockFetch).toHaveBeenCalled();
   });
-});
+});