Plan stale wfctl DNS marker cleanup

[intel352]

Summary

• report stale wfctl-managed TXT markers as DNS record deletions during Diff even when manage_unlisted=false
• keeps the cleanup scoped to _workflow-dns-managed records containing wfctl marker metadata and only when desired state includes a current marker
• adds a regression matching gigbagg.rocks duplicate marker state

Verification

• GOWORK=off go test ./internal/drivers -run 'TestDNSDriver_(DiffDetectsStaleWorkflowManagedMarkersWhenUnlistedRecordsArePreserved|UpdateDeletesStaleWorkflowManagedMarkersWhenUnlistedRecordsArePreserved|RecordBodiesSendQuotedTXTContentToCloudflare)' -count=1
• GOWORK=off go test ./...
• GOWORK=off go test ./... -race -count=1
• git diff --check

Context

A gocodealone-dns plan using v0.1.20 did not include gigbagg.rocks, so apply would not enter the stale-marker cleanup path for already-converged resources. This makes the cleanup visible in the plan and executable by apply.

[Copilot]

Pull request overview

This PR makes stale wfctl-managed _workflow-dns-managed TXT marker records visible in Diff (as deletions) even when manage_unlisted=false, aligning plan output with the existing apply-time cleanup behavior.

Changes:

• Track whether the desired state includes a current workflow-managed marker, and when manage_unlisted=false report any other workflow-managed markers in the zone as deletions during Diff.
• Add a regression test covering the “duplicate marker” scenario (e.g., gigbagg.rocks) where one marker is desired and another is stale.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/drivers/dns.go	Extends diffRecords to surface stale workflow-managed marker deletions when unlisted records are otherwise preserved.
internal/drivers/dns_test.go	Adds regression coverage ensuring Diff flags stale workflow marker records as deletions under manage_unlisted=false.

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