link-checker: viewing failed links requires extra click

When link-checker finds a broken link, the report isn't immediately viewable.
Improve the reporting:
- Regular output doesn't need to print the config - hide it in a debug flag
- Combine the error and list of links
- If possible, show details in the PR to avoid having to click to view details

Start by locating the link-checker entry point and its report-generation path. Review how regular output, configuration details, errors, and link lists are currently presented. Done means configuration is debug-only, each error is combined with its links, and PR details are shown directly where possible.

Written by the indexing model from the issue text.