fix: verify-references installs TS deps; sync-check covers expansion tests; template gitignore and passWithNoTests

verify-references ran a bare `npx vitest run` in the staged reference, which
fetched an unrelated vitest that could not load the reference config. It now
installs the reference's devDependencies first. sync-check also checks each
module's expansion/tests against ### headings in expansion/README.md.

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

tools/sync-check.mjs

@@ -1,24 +1,31 @@
 #!/usr/bin/env node
 // Verifies Rust tests, TS tests and scenarios.md list identical test names per module.
+// A module's Expansion Drop (expansion/tests/{rust,ts}, scenarios as `### test_…`
+// headings in expansion/README.md) is checked the same way, as a separate set.
+import { join } from "node:path";
 import { moduleDirs, testNames, scenarioNames } from "./lib.mjs";
 
 const problems = [];
-for (const mod of moduleDirs()) {
+function check(label, path, scenarioFile) {
   const sets = {
-    rust: testNames(mod.path, "rust"),
-    ts: testNames(mod.path, "ts"),
-    scenarios: scenarioNames(mod.path),
+    rust: testNames(path, "rust"),
+    ts: testNames(path, "ts"),
+    scenarios: scenarioNames(path, scenarioFile),
   };
-  if (Object.values(sets).every((s) => s.length === 0)) continue;
+  if (Object.values(sets).every((s) => s.length === 0)) return;
   const all = new Set(Object.values(sets).flat());
   for (const name of [...all].sort()) {
     for (const [where, names] of Object.entries(sets)) {
-      if (!names.includes(name)) {
-        problems.push(`module ${mod.num}-${mod.slug}: ${name} missing from ${where}`);
-      }
+      if (!names.includes(name)) problems.push(`${label}: ${name} missing from ${where}`);
     }
   }
 }
+
+for (const mod of moduleDirs()) {
+  const label = `module ${mod.num}-${mod.slug}`;
+  check(label, mod.path, "scenarios.md");
+  check(`${label} expansion`, join(mod.path, "expansion"), "README.md");
+}
 if (problems.length) {
   console.error("sync-check: mismatches\n" + problems.map((p) => "  " + p).join("\n"));
   process.exit(1);