Add internal link checker

[pedro-psb]

Although link checking will not be strictly static (it may try to build the site), I'd like to put it under a general linting category of commands. For now, the only "linter" would be internal link checker (should we add external as well?)

# run all linting on all code
pulp-docs lint

# run link-check on all code
pulp-docs lint --linters link-check

# run link-check on pulp-docs only
pulp-docs lint --linters link-check --repos pulp-docs

Approaches Considered

• Leverage mkdocs validation + tricks to select only links from a single repository
• Find another link checker

Current plan - march 2026

Just add a program that perform the linkcheking.

1. (this) Add linkchecker cli tool #174
2. Distribute the linkcheck make runner and CI linting via Create managed files for pulp-docs on ALL components #183

Plan - september 2025

• Add linkchecker cli tool #174
• Add a pulp-docs configuration for members - Plugins can opt-in to new features (docs/pulpdocs.yml)
• Add an optional link-check job to docs CI - If link-checking in enabled for a member it'll be enforced

[pedro-psb]

I decided to make a simple link checker because I've tried some existing link checkers, and they had some shortcomings for our multi-repo setup.
In particular:

1. Tool for internal links relies on relative markdown links, which we don't use (we use the site:)
2. Hard to filter only links internal to the plugin vs to other plugins (for checking a component in isolation)
3. Requires building the site (makes it hard to show exactly where in the source the broken link is).