feat: log tree from Module 2 (logTree / log_tree); SpellGrid CLIs print Log:

Engine events carry the nesting depth they were recorded at; the harness
prints the log as an indented tree. New tests test_02_log_tree_shows_nesting
and test_03_log_tree_death_phase; both SpellGrid CLIs print the tree of the
last command's Sequences under a Log: line.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

course/04-interceptors/reference/ts/src/engine/queue.ts

@@ -166,8 +166,11 @@ function react(world: World, events: Event[]): void {
           ? positionLeftOf(world, world.ownerOf(source), event.before)
           : world.boardIndex(source);
       const actions = trigger.effect(new Ctx(world, world.ownerOf(source), source, undefined, position));
+      // The trigger's consequences are one level deeper in the log tree.
+      world.openBlock();
       // Depth-first: each action, and every reaction it causes, finishes before the next.
       for (const action of actions) perform(world, action);
+      world.closeBlock();
     }
   }
 }