feat: summoned minions enter the grid in Module 10 (a fourth seam; Clay Golem, Clay Shard)

Summoned records its summoner (the minion whose trigger is resolving) inside
the engine; the harness log is unchanged. When a Sequence ends, SpellGrid
writes spawned text, places each summoned minion with a noun on its
summoner's tile, removes the dead, reparses and syncs rule auras.

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

course/10-spellgrid/reference/rust/tests/cli.rs

@@ -109,5 +109,5 @@ fn cli_numbers_are_plain_digits() {
     // "+2" is not a number, so the chooser takes the first option.
     let level = include_str!("../levels/l2-spliced-corpse.json");
     let (_, out) = play(level, &["c Graft", "+2", "1", "1", "q"]);
-    assert!(out.contains("Hand: Ember Moth (Assembled)"), "{out}");
+    assert!(out.contains("Hand: Clay Golem (Assembled)"), "{out}");
 }