feat(domains): add TrackingCAA record support

[rehanvdm]

Summary

The Domains API now returns an extra DNS record on POST /domains and GET /domains/:id when a tracking subdomain is configured and the customer's root domain has CAA records that would prevent AWS from issuing a certificate for the tracking subdomain:

{
  "record": "TrackingCAA",
  "name": "",
  "type": "CAA",
  "ttl": "Auto",
  "value": "0 issue \"amazon.com\"",
  "status": "verified"
}

The Record TypedDict already accepts arbitrary string values for record and type, so no source change is required beyond a docstring update — the record deserializes today. This PR extends the test fixtures (sync + async) so the new record is exercised, and updates the docstring to list TrackingCAA as a known example value.

Test plan

• pytest tests/domains_test.py tests/domains_async_test.py — 32 passed (including the new TrackingCAA assertions in test_domains_create_with_tracking_subdomain, test_domains_get_with_tracking_fields, and their async equivalents)

Tracking: Linear ENG-4843

🤖 Generated with Claude Code

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Summary by cubic

Adds TrackingCAA DNS record support in domain responses when a tracking subdomain is set and root-domain CAA would block AWS from issuing the tracking certificate. Aligns with Linear ENG-4843.

• New Features

  • Updated Record docstring to include TrackingCAA.
  • Extended sync and async tests to cover the new CAA record (value: 0 issue "amazon.com") and ensure it deserializes correctly.

• Dependencies

  • Bumped resend version to 2.28.1.

^{Written for commit 86d23b3. Summary will update on new commits.}

[cubic-dev-ai]

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