[heyanay2105]

Self-hosted platforms can't use project custom domains today. void domain add returns 501 because nothing turns the capability on, and the API always hands out cname.void.app as the CNAME target.

• Adds --custom-domains to platform install, upgrade, and repair. It needs a dedicated application zone.
• The domains API now uses the install's SITE_DOMAIN for the CNAME target and the reserved suffix, like the rest of the API does.
• The runtime token link already asks for SSL and Certificates: Edit, and the preflight already checks it, so no changes there.
• Docs: a Project Custom Domains section with the one-time Cloudflare for SaaS setup, plus the CLI reference and the credentials note.

Tested end to end on our own install:

• Built with install:void-dev and upgraded from 1.1.11 with void-dev platform upgrade --runtime … --custom-domains.
• Added an apex and a www domain. Both went active with HTTPS and serve the app.
• cli-unit and platform-* tests pass.

[cpojer]

Awesome, thank you!