OnStart takes a script name, and OnFinale joins it

The opening a game plays was the one piece of content that had to be
assembled in the wiring, because OnStart wanted an Action. It takes the
name of a registered Script now, so an opening is a Script like any
other, and Validate rejects a name that is not there.

OnFinale names the closing script and queues it straight after the start
one — what a "boot into the ending" debug flag wants.

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

core.dsl.go

@@ -34,8 +34,11 @@ func Run(g *Game) error {
 	if s.OnEnter != nil {
 		seq = append(seq, s.OnEnter)
 	}
-	if g.onStart != nil {
-		seq = append(seq, g.onStart)
+	if g.onStart != "" {
+		seq = append(seq, RunScript(g.onStart))
+	}
+	if g.onFinale != "" {
+		seq = append(seq, RunScript(g.onFinale))
 	}
 	if len(seq) > 0 {
 		g.queueAction(Seq(seq...), "init")