* [management] Return the reason when custom domain validation fails
The validate endpoint returned an empty 202 and ran the check in a
goroutine, so a failed verification only reached the management log.
Run the check in the request and return 204 or 412 with a classified
reason. Resolver errors are not forwarded.
* [management] Address review feedback on custom domain validation
Pass the request context to the lookup and store calls now that the
check runs in the request, compare the self-resolved name
case-insensitively, document the 412 like the other entries, and
check the returned error in the existing tests.
* [management] Match custom domain CNAME targets case-insensitively
DNS names are case-insensitive, so a CNAME pointing at the cluster in
different casing should validate instead of failing as a mismatch.
* [management] Add validation timeout
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Co-authored-by: DevBot NetBird <91386968+netbirddev@users.noreply.github.com>
Prevent unvalidated registrations from reserving domain names indefinitely.
Give pending registrations a 48-hour validation window and clean up expired entries at startup and every 60 minutes. Emit CustomDomainValidationExpired for each deletion and preserve registrations referenced by services.
Reject validation after expiry and prevent concurrent validation from recreating deleted registrations. Normalize domain names with the shared parser before registration.
Migrate existing pending registrations to receive a fresh 48-hour validation window.
