fix(tools): stage course cards from M5, audit noun words without flagging identifiers, Node<24.2 main guard, rename-proof expansion-check, safe check-links

- cardDirs: course/cards only from Module 5 (spec 6.2a); fixture modules 04/05 and tests
- coupling-audit: noun words match as UPPERCASE, PascalCase or a whole string literal;
  lowercase identifiers like key/flag pass; card names keep every variant
- isMain() argv guard replaces import.meta.main in coupling-audit and verify-references;
  engines.node >=22
- expansion-check: git diff --no-renames so moving engine code into content fails
- start-module and other tools: clear error when .course.json is missing
- check-links: malformed URLs reported as invalid URL instead of throwing

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

package.json

@@ -3,6 +3,9 @@
   "private": true,
   "type": "module",
   "license": "MIT",
+  "engines": {
+    "node": ">=22"
+  },
   "scripts": {
     "test:tools": "node --test tools/test/*.test.mjs",
     "check": "node tools/sync-check.mjs",