Add regfish-dns provider

[tobiashaigis]

Summary

Added provider for Regfish DNS

Validation

• dotnet build -c Release ./src
• dotnet format --verify-no-changes --verbosity detailed --no-restore ./src

[Copilot]

Pull request overview

Adds a new DNS provider integration for Regfish DNS so Acmebot can create/delete TXT records for DNS-01 challenges via the Regfish API.

Changes:

• Introduce RegfishProvider implementation with an internal RegfishClient for zone/record operations.
• Add RegfishOptions and expose it via AcmebotOptions.
• Register the new provider in Program.cs DNS provider setup.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/Acmebot.App/Providers/RegfishProvider.cs	Implements Regfish DNS provider + HTTP client wrapper for zones/records
src/Acmebot.App/Program.cs	Registers RegfishProvider when Acmebot:Regfish options are configured
src/Acmebot.App/Options/RegfishOptions.cs	Adds options model for Regfish API key
src/Acmebot.App/Options/AcmebotOptions.cs	Exposes Regfish configuration slot on main options

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

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[Copilot]

IsMatchingTxtRecord contains a special-case for records whose API name is "@" (zone apex), but GetAbsoluteRecordName always formats ${relativeRecordName}.${zoneName}. so it will never pass recordName == zoneName (and will produce values like "@.example.com." / ".example.com." instead). This makes apex matching inconsistent and would prevent DeleteTxtRecordAsync from removing apex TXT records if relativeRecordName is "@" or empty. Consider handling "@"/empty explicitly in GetAbsoluteRecordName (and/or adjusting IsMatchingTxtRecord) so the representation is consistent.

Suggested change

	private static string GetAbsoluteRecordName(string zoneName, string relativeRecordName) => $"{relativeRecordName}.{zoneName}.";
	private static string GetAbsoluteRecordName(string zoneName, string relativeRecordName)
	{
	var normalizedZoneName = NormalizeName(zoneName);
	if (string.IsNullOrWhiteSpace(relativeRecordName) || string.Equals(relativeRecordName.Trim(), "@", StringComparison.Ordinal))
	{
	return $"{normalizedZoneName}.";
	}
	var normalizedRelativeRecordName = NormalizeName(relativeRecordName);
	return $"{normalizedRelativeRecordName}.{normalizedZoneName}.";
	}