Good first issue: add Markdown link verification to the public gates

## Why The P0.1 documentation now contains multiple contributor and contract entry points. Local links were checked during delivery, but link integrity is not yet enforced by `npm run verify`. ## Scope Add a dependency-free Node.js verification script that checks relative Markdown links across the public repository and wire it into `npm run verify`. ## Acceptance criteria - [ ] Scans tracked `*.md` files while ignoring `.git` and `node_modules`. - [ ] Resolves relative file and directory links from the Markdown file location. - [ ] Ignores `http:`, `https:`, `mailto:`, and same-page anchors. - [ ] Reports every missing target with source file and target. - [ ] Runs on Windows and Linux with Node.js 20 and 22. - [ ] Adds at least one fixture or test proving a broken link fails. - [ ] `npm run verify` passes. - [ ] Commit includes DCO sign-off (`git commit -s`). ## First step Comment `I would like to work on this` before opening a PR. Keep the implementation dependency-free and focused on relative-link existence; external URL crawling is out of scope.