Description:
The repository lacked automated documentation quality checks, leading to inconsistent Markdown styling and the risk of broken external links slipping into PRs. This feature request introduces standardized linting and link validation to improve docs reliability and contributor experience.

Proposed solution:
Add a GitHub Actions workflow to run Markdown linting and external link checks on all PRs touching .md files.

Add shared configurations for markdownlint and lychee at the repo root.

Document how to run these checks locally in CONTRIBUTING.

Acceptance criteria:

A CI workflow runs on PRs and fails when markdown rules are violated or external links are broken.
Linting and link-check configs live at repo root and are used by the workflow.
CONTRIBUTING includes clear instructions for running these checks locally.