feat: native SSH delegation via tea.ExecProcess + Gruvbox palette

Phase A — Tamagosh-inspired redesign:
- Replace goroutine-based SSH (crypto/ssh) with tea.ExecProcess + native ssh binary
- Zero-lag SSH: native binary pegang TTY langsung, ga ada Go buffering
- Password auth via sshpass -e (SSHPASS env)
- Key auth via ssh -i <tmpfile> + SSH_ASKPASS for passphrase
- ControlMaster sockets for fast reconnect
- Add askpass subcommand for SSH_ASKPASS support
- Gruvbox Material Dark Hard palette for comfortable viewing
- Clean up old session messages (openSessionMsg, sessionOutputMsg, sessionDoneMsg)
- Remove 354-line session.go, replace with 150-line ssh.go

pkg/tui/messages.go

@@ -12,16 +12,13 @@ import (
 // quitMsg signals the TUI to exit
 type quitMsg struct{}
 
-// openSessionMsg signals the TUI to open a new SSH session tab
-type openSessionMsg struct {
+// sshConnectToMsg signals the TUI to connect to a host via native SSH
+type sshConnectToMsg struct {
 	host *models.Host
 }
 
-// sessionOutputMsg carries SSH output to the TUI renderer
-type sessionOutputMsg string
-
-// sessionDoneMsg signals that a session has ended
-type sessionDoneMsg struct {
+// sshExitMsg signals that a native SSH session has ended
+type sshExitMsg struct {
 	err error
 }