feat: Module 11 becomes 13; diff-tracks fuzzer; align the two reference tracks

- Rename course/11-break-your-engine to 13-break-your-engine and update every
  link and mention; start-module explains that Module 13 has no tests to start.
- tools/diff-tracks.mjs (npm run diff:tracks): stages both references of a
  module, generates a seeded random SpellGrid level and script per seed, pipes
  it to the Rust and TypeScript CLIs and diffs their output; crashes on one or
  both sides fail. stagePlay takes a module number.
- register_assembled: the TypeScript track compared only the text of an
  existing Assembled card, so a base re-registered with a new cost (or a
  different split) silently rewrote the earlier card. It now compares every
  field the engine reads, as Rust does (Modules 5-10).
  New test_05_assemble_never_rewrites_an_earlier_card.
- SpellGrid CLIs: coordinates and chooser numbers are 1-9 plain digits in both
  tracks (Rust accepted signs, TypeScript accepted "+2", "0x2", "1e0"); Rust
  quotes card names verbatim instead of with Debug escapes; Rust joins the
  minion list with "; " instead of rewriting ", ". Two new CLI tests per track.

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

tools/start-module.mjs

@@ -15,6 +15,9 @@ if (track !== "rust" && track !== "ts") fail(`bad track in .course.json: ${track
 const mods = moduleDirs();
 const mod = mods.find((m) => m.num === num);
 if (!mod) fail(`no module ${num} in ${courseRoot()}`);
+if (!testFiles(mod.path, "rust").length && !testFiles(mod.path, "ts").length) {
+  fail(`Module ${num} has no tests to start: it is made of reading and exercises. Open ${join(mod.path, "lesson.md")}.`);
+}
 
 if (num !== "01") {
   const prevNum = String(Number(num) - 1).padStart(2, "0");