Add --help output and test for hygiene checks

Support printing concern-specific help for the split hygiene entrypoints and add a test.

- scripts/check-repo-hygiene.mjs: handle `--help`/`-h` early and print a formatted usage message (formatUsage) then exit 0. parseArgs now recognizes help flags. The usage text includes the selected concern name and common options (--root, --changed-files, --diff-file, --only).
- scripts/check-repo-concerns.test.mjs: add a test that invokes each entrypoint with `--help` and asserts the process exits successfully and prints usage/help text including the concern-specific name and expected options.

This prevents the checks from running when users request help and ensures the help text is descriptive for each concern.

Author: PatrickJS

scripts/check-repo-concerns.test.mjs

@@ -110,3 +110,32 @@ test("repo security entrypoint reports only prompt security failures", () => {
     rmSync(root, { recursive: true, force: true });
   }
 });
+
+test("split check entrypoints print concern-specific help without running checks", () => {
+  const root = makeFixture();
+  const expectedNames = {
+    readme: "README hygiene",
+    rules: "Rule hygiene",
+    issues: "Issue template policy",
+    security: "Repo security",
+  };
+
+  try {
+    write(root, "README.md", "### Other\n\n- [Missing](./rules/missing.mdc)\n");
+    write(root, "rules/bad.mdc", "# Missing frontmatter\n");
+
+    for (const [concern, entrypoint] of Object.entries(entrypoints)) {
+      const result = run(entrypoint, root, ["--help"]);
+
+      assert.equal(result.status, 0);
+      assert.match(result.stdout, /Usage:/);
+      assert.match(result.stdout, new RegExp(`${expectedNames[concern]} check`));
+      assert.match(result.stdout, /--root/);
+      assert.match(result.stdout, /--changed-files/);
+      assert.match(result.stdout, /--diff-file/);
+      assert.equal(result.stderr, "");
+    }
+  } finally {
+    rmSync(root, { recursive: true, force: true });
+  }
+});

scripts/check-repo-hygiene.mjs

@@ -5,6 +5,11 @@ import { join, normalize, resolve } from "node:path";
 import { githubBlobPrefix, githubRawPrefix } from "./repo-config.mjs";
 
 const args = parseArgs(process.argv.slice(2));
+if (args.help) {
+  console.log(formatUsage(args.only));
+  process.exit(0);
+}
+
 const root = resolve(args.root ?? process.cwd());
 const changedFiles = args.changedFiles
   ? readLines(resolve(root, args.changedFiles))
@@ -61,7 +66,9 @@ function parseArgs(argv) {
   const parsed = {};
   for (let i = 0; i < argv.length; i += 1) {
     const arg = argv[i];
-    if (arg === "--root") {
+    if (arg === "--help" || arg === "-h") {
+      parsed.help = true;
+    } else if (arg === "--root") {
       parsed.root = argv[++i];
     } else if (arg === "--changed-files") {
       parsed.changedFiles = argv[++i];
@@ -76,6 +83,24 @@ function parseArgs(argv) {
   return parsed;
 }
 
+function formatUsage(only) {
+  const selected = parseConcerns(only);
+  const checkName = describeConcerns(selected);
+
+  return [
+    `${checkName} check`,
+    "",
+    "Usage: node scripts/check-repo-hygiene.mjs [options]",
+    "",
+    "Options:",
+    "  --root <path>           Repository root to check. Defaults to cwd.",
+    "  --changed-files <file>  Newline-delimited changed files, relative to root.",
+    "  --diff-file <file>      Unified diff file used for README-only checks.",
+    "  --only <concerns>       Comma-separated concerns: readme, rules, issues, security.",
+    "  -h, --help              Show this help.",
+  ].join("\n");
+}
+
 function parseConcerns(value) {
   const validConcerns = new Set(["readme", "rules", "issues", "security"]);
   const selected = new Set((value ?? "readme,rules,issues")