Module markdownlint 

Markdown linting and formatting gate (native Rust, no shell-out).

This is the MVP rule-set tracked under issue #549. It covers the markdownlint-style rules that catch the bulk of authoring drift without requiring a full upstream markdownlint-rs integration — the depth-of-coverage roadmap calls out adding the upstream port once it stabilises for 2026 toolchains.

Rules enforced:

• MD009 — no trailing whitespace at end of line.
• MD010 — no hard tabs (use spaces).
• MD025 — at most one top-level # heading per file.
• MD034 — no bare http:// / https:// URLs (must be in [text](url) or <url> form).
• MD041 — file must start with a top-level heading (or YAML frontmatter followed by one).

Scans the content directory (<site>/../content or the sibling content/ dir). When neither exists the gate emits an info note and skips — matches the behaviour of the docs gates.

Structs

MarkdownlintGate

Markdown linting + formatting gate.