Add town session cycling for mayor/deacon (C-b n/p)

- Create gt town next/prev commands for cycling between town-level sessions
- Add SetTownCycleBindings() to tmux package
- Wire up bindings when starting mayor and deacon sessions

Now mayor and deacon have the same C-b n/p cycling behavior as crew workers.

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

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

internal/cmd/deacon.go

@@ -188,6 +188,9 @@ func startDeaconSession(t *tmux.Tmux) error {
 	theme := tmux.DeaconTheme()
 	_ = t.ConfigureGasTownSession(DeaconSessionName, theme, "", "Deacon", "health-check")
 
+	// Set up C-b n/p keybindings for town session cycling (non-fatal)
+	_ = t.SetTownCycleBindings(DeaconSessionName)
+
 	// Launch Claude directly (no shell respawn loop)
 	// Restarts are handled by daemon via ensureDeaconRunning on each heartbeat
 	// The startup hook handles context loading automatically