feat: add ForwardAgent support

[skyhancloud]

Adds optional SSH agent forwarding support to lazyssh. Users can now enable ForwardAgent per server entry via the Add/Edit form. When enabled, the app writes ForwardAgent yes to the host block and uses -A in ad‑hoc SSH command generation.

[skyhancloud]

@Adembc

[Adembc]

Thanks for your PR!
In this update #45 , I’ve changed the way we parse and write ssh config. The old approach was overwriting unsupported fields, comments, and formatting, but now we can safely extend support for additional fields.

I’ll open an issue to track adding support for more fields. If you’d like, feel free to pick it up and submit another PR.