Go implementation of the LocalSend v2.1 protocol for secure,
cross-platform file sharing.

* Complete LocalSend v2.1 Protocol -- Works with LocalSend apps
* Secure -- HTTPS with certificates, optional PIN protection
* Fast Discovery -- Multicast UDP + HTTP fallback
* Multi-file Transfers -- Send multiple files concurrently
* Web Share -- Share files via browser download link
* Clipboard Integration -- Incoming text/plain transfers copied
  to clipboard automatically
* Metadata Preserved -- File timestamps preserved on transfer