v3 port. Customer PDF controllers resolved the target document by raw
mailable_id ignoring mailable_type, and skipped expiry on the JSON endpoints.
- Resolve via $emailLog->mailable + assert the expected type (404) to close
cross-type disclosure.
- Enforce isExpired() (403) on every public path incl. the JSON endpoints.
- Harden EmailLog::isExpired() against a null/unresolvable mailable.
Adds tests for cross-type 404, JSON-path expiry 403, and the valid path.
