Cannot suppress auto-generated links for type=github

[ManningWorks]

For projects where type: 'github' but you don't want the auto-generated links (e.g. a personal site that already IS the live URL), there's no way to suppress them.

Repro: Set links: { github: '', live: '' } — Zod validation fails with Invalid url before normalisation even runs.

Expected: Either:

1. Allow null or empty string to suppress a link (treat it as "not provided")
2. Add an excludeLinks option or similar to prevent auto-generation for specific link types
3. Document that type: 'github' always generates links and override doesn't cover them

Workaround: None that work cleanly — override only covers name/tagline/description/stack. For a personal site that IS the live URL, having auto-generated "github" and "live" links pointing back to the same site is noise.

Version: @manningworks/projex latest

[ManningWorks]

Adding a useLiveLinkFromGithub field (or similar) to the project config would solve this cleanly:

// Opt in to the auto-generated live link
{ repo: 'ManningWorks/my-site', useLiveLinkFromGithub: true }

// Suppress it without needing to clear the homepage on GitHub
{ repo: 'ManningWorks/my-site', useLiveLinkFromGithub: false }

Default could be true for backward compat, or false if auto-generated links shouldn't appear without explicit opt-in.

Same logic could apply to useGithubLinkFromRepo for the auto-generated GitHub link.