rpm 4.14 (RHEL/CentOS/Rocky 8) cannot import an Ed25519 public key at all:
the import fails and package verification reports SIGNATURES NOT OK. RHEL 8
is supported until 2029 and is a realistic target for a signed package repo,
so the Ed25519 key excludes a large part of the rpm audience.
Publish an RSA-4096 signing key as 3proxy-release-key.asc and keep the old
Ed25519 key as 3proxy-release-key-ed25519.asc so artifacts up to 0.9.9 stay
verifiable. Workflows derive the key id from the imported secret key, so no
workflow change is needed.
GPG signing of rpm packages and detached signatures for deb packages and
for the SHA256SUMS files, using GPG_PRIVATE_KEY / GPG_PASSPHRASE secrets.
Checksums are published as release assets.
Build provenance is attested before the assets are uploaded, so a failed
attestation does not leave unattested files published.
Workflow permissions are read-only, write permissions are requested per
job only where they are used.
