The subkey 16D5D4DFC0C36022 lives only on the project's machines,
with its own passphrase, and expires together with the primary key
on 2027-01-31
- Add the subkey to the table in OPENPGP.md
- Replace the 6-month expiry policy for external subkeys: they now
follow the yearly update and are revoked as "retired" at project end
- Export the updated public key and a dated snapshot
- Re-sign OPENPGP.md
