age reference fixture

reference.age was produced by the reference age implementation (v1.3.1):

printf 'openagents account export fixture\n' > plain.txt
age --encrypt -r age1ja3nzz0wlmuqvsfhrx7w4kq00knnmu3ur32y47734k5javp4cqnqumg72a \
  -o reference.age plain.txt

test/openagents/data_rights/age_test.exs decrypts it with OpenAgents.Test.AgeDocument, the decryptor written from the specification. That direction is what pins our reading of the format to the reference implementation, so the encryption round trip means something where the age binary is not installed.

The identity is a throwaway generated for this fixture and protects nothing. It lives in the test as @fixture_secret rather than in a file, so nothing here looks like a credential in use.