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

cmd/hostkeeper/main.go

@@ -11,6 +11,13 @@ var (
 )
 
 func main() {
+	// SSH_ASKPASS support: hostkeeper askpass
+	// Called by the SSH_ASKPASS script we create for key passphrases.
+	if len(os.Args) == 2 && os.Args[1] == "askpass" {
+		fmt.Print(os.Getenv("HK_PASSPHRASE"))
+		return
+	}
+
 	if err := Execute(); err != nil {
 		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
 		os.Exit(1)