feat: Add documentation files including Code of Conduct, Contributing guidelines, and Security policy; update Markdown linting configuration and scripts

scripts/lint-markdown.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+#
+# Lint all Markdown files in the repository.
+# Config, globs, and ignores are defined in .markdownlint-cli2.jsonc.
+#
+# Usage:
+#   ./scripts/lint-markdown.sh          # check
+#   ./scripts/lint-markdown.sh --fix    # auto-fix
+#
+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"
+else
+    LINT_CMD="npx --yes markdownlint-cli2"
+fi
+
+echo "Linting Markdown files..."
+$LINT_CMD "$@"
+echo "Markdown lint passed."