feat: module 05 assemble

Cards become JSON data in course/cards (one file per card, validated
against card.schema.json and the catalog); the M5 references load them
via registerCards and interpret effects, replacing content closures.
Adds assemble(base, donor, half), the assemble/buffHand effects with an
injected chooser, Fleshshape as the data-only Expansion Drop, and stages
course/cards in verify-references and start-module.

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

tools/test/fixtures/course/cards/test-fixture.json

@@ -0,0 +1 @@
+{"name":"Test Fixture","type":"minion","cost":1,"attack":1,"health":1,"split":0,"text":[]}