Use repo config for minimizer URLs

[lykimq]

• Use all minimizer links from repo_config.minimizer_url instead of hardcoded Rocq URLs.
• GitHub webhook handlers (comment minimize, issue opened, CI minimize) look up the URL per repo and skip minimization when it is not configured.
• CI minimization reply text uses a shared link helper, and GitLab pipeline auto-minimize receives the same config value.
• Tests cover config parsing and link formatting with and without a URL.