Make the certificate domain configurable

[DrNefarius]

Summary
The server certificate hardcodes pi.hole as a SAN, which doesn't match setups that use a different local domain. This makes the domain configurable while defaulting to pi.hole, so existing installs are unaffected.

What changed

• Configurable certificate domain, resolved in this order: LOCAL_HTTPS_DOMAIN env var → --domain flag (--install/--configure/--renew) → persisted state → Pi-hole's webserver.domain (auto-detected on fresh installs) → default pi.hole.

• Interactive prompt during install/configure (pre-filled, skipped when set via env/flag or non-interactive).

• Domain is persisted in state and shown in --status, so renewals reuse it.

• install.sh forwards LOCAL_HTTPS_DOMAIN; README updated with a "Custom domain" section.

Notes

• Backward compatible — default stays pi.hole; installs without a saved domain fall back to it.

[luizbizzio]

Thanks, this is a useful improvement. I’ll merge it and do a small follow-up pass to harden the domain validation and CLI option handling before the next release.