Add gt recycle command for instant session hot-reload

Uses tmux respawn-pane to kill and restart agent sessions in place,
bypassing the handoff/manager flow for quick context cycling.

Supports local recycle (current session) and remote recycle (other
roles) with automatic client switching.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/tmux/tmux.go

@@ -544,3 +544,11 @@ func (t *Tmux) SetMailClickBinding(session string) error {
 		"display-popup", "-E", "-w", "60", "-h", "15", "gt mail peek || echo 'No unread mail'")
 	return err
 }
+
+// RespawnPane kills all processes in a pane and starts a new command.
+// This is used for "hot reload" of agent sessions - instantly restart in place.
+// The pane parameter should be a pane ID (e.g., "%0") or session:window.pane format.
+func (t *Tmux) RespawnPane(pane, command string) error {
+	_, err := t.run("respawn-pane", "-k", "-t", pane, command)
+	return err
+}