Add markdown linting tools and scripts

- Create package.json to manage markdownlint-cli2 as a dev dependency.
- Add PowerShell script for linting Markdown files with options for fixing issues.
- Update shell script to prefer locally installed markdownlint-cli2 or fallback to npx.

scripts/lint-markdown.sh

@@ -2,6 +2,8 @@
 #
 # Lint all Markdown files in the repository.
 # Config, globs, and ignores are defined in .markdownlint-cli2.jsonc.
+# The linter version is pinned in package.json — run `npm install` once,
+# or just use `npm run lint:md` / `npm run lint:md:fix` directly.
 #
 # Usage:
 #   ./scripts/lint-markdown.sh          # check
@@ -12,11 +14,12 @@ set -euo pipefail
 REPO_ROOT="$(cd "$(dirname "$0")/.." && pwd)"
 cd "$REPO_ROOT"
 
-# Resolve markdownlint-cli2 binary
-if command -v markdownlint-cli2 &>/dev/null; then
-    LINT_CMD="markdownlint-cli2"
+# Prefer the locally installed (version-pinned) linter; fall back to a one-off
+# npx install of the same version pinned in package.json.
+if [ -x "node_modules/.bin/markdownlint-cli2" ]; then
+    LINT_CMD="npx --no-install markdownlint-cli2"
 else
-    LINT_CMD="npx --yes markdownlint-cli2"
+    LINT_CMD="npx --yes markdownlint-cli2@0.23.0"
 fi
 
 echo "Linting Markdown files..."