The opening is a script now, not a slice in the wiring

bootOpening built its actions in boot.go and appended the finale by hand,
which made the one thing a player sees first the only content not
authored as content. inkwell's OnStart takes a script name now, so the
opening moves to script.opening.go and boot names it.

The -finale flag becomes OnFinale, the engine's hook for a closing script
queued after the start one, so the branch is a hook rather than a slice
append. bootOpening's start parameter had been dead for a while; it goes
with the function.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

inc/names.manager.go

@@ -20,6 +20,7 @@ const (
 )
 
 const (
+	ScriptOpening    = "opening"
 	ScriptTapeInsert = "tape_insert"
 	ScriptFinale     = "awakening_finale"
 )