Verification Public Key

Publish the Ed25519 public key for offline third-party verification.

Returns the raw public key as base64url + the key_id + the algorithm so a verifier can reconstruct an Ed25519PublicKey and check any certificate's signature without trusting Badge's server (§9 Q2).

When verification is disabled or the signing key is unavailable in a non-dev env, returns an empty keys list (the document still exists — well-known endpoints should resolve, not 404) so a verifier sees "no published key" rather than a server error.

The document is static for the life of a key — served with a 1h Cache-Control so CDNs/clients don't re-fetch on every verification (security-auditor LOW follow-up). The per-request public-key derivation is ~µs (Ed25519), so we keep it un-memoized to stay correct across a key rotation rather than caching in-process.