Fix: kill stale tmux session as separate command, not in chain

tmux aborts the entire command chain when kill-session fails (no
existing session). This caused 'no current target' error on Linux.

The kill-session is now a separate exec.Command() call before
starting the tmux chain, ignoring any error.

SPEC.md

@@ -89,7 +89,8 @@ not cover: **redeploy** and **secrets diff**.
 Example startup command (generic placeholders):
 
 ```
-tmux kill-session -t kctl \; \
+# Kill stale session first (separate command — tmux aborts on kill-session error).
+tmux kill-session -t kctl
 tmux new-session -d -s kctl \
   -- "kctl-tui panel --context=$CTX_A --ns=$NS --team=$TEAM" \; \
   set-option -t kctl remain-on-exit on \; \

cmd/kctl-tui/full.go

@@ -277,8 +277,10 @@ func (m *fullModel) startTmuxSession() tea.Cmd {
 	ctxA := m.cfg.ResolveContext(envA, m.selectedContext)
 	k9sCmdA := fmt.Sprintf("k9s --context %s -n %s", ctxA, m.selectedNamespace)
 
+	// Kill stale session first (ignore error if none exists).
+	exec.Command("tmux", "kill-session", "-t", "kctl").Run()
+
 	args := []string{
-		"kill-session", "-t", "kctl", ";", // ignore error if no session exists
 		"new-session", "-d", "-s", "kctl",
 		"--", panelCmd, ";",
 		"set-option", "-t", "kctl", "remain-on-exit", "on", ";",