Allow SSH connections to be routed through SOCKS5 or HTTP CONNECT proxies.
Backend:
- Add ProxyType, ProxyHost, ProxyPort, ProxyUsername, ProxyPassword to SSHConfig
- dialTarget() dispatches to direct TCP, SOCKS5, or HTTP CONNECT based on config
- SOCKS5: uses golang.org/x/net/proxy with optional username/password auth
- HTTP CONNECT: sends CONNECT request with optional Basic auth, validates 200 OK
- Proxy dialling replaces ssh.Dial for non-jump-host connections; the resulting
net.Conn is passed to ssh.NewClientConn for the SSH handshake
Frontend:
- Add Proxy section to SSH profile editor (collapsed by default)
- Proxy type selector: None / SOCKS5 / HTTP CONNECT
- Host, port, username, password fields
- Collect proxy values on save