Regenerate cosign key pair for image signing

The build workflow requires a cosign public/private key pair to sign
the container image. The private key is stored as the SIGNING_SECRET
GitHub secret.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: SecAI-Hub

cosign.pub

@@ -1,4 +1,4 @@
 -----BEGIN PUBLIC KEY-----
-MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEP42H58yIV98/GrQkArabAnsfLLjr
-MI848NLkUwI29cEnc6K8qVZESVrqxP0mB9e4NCSJ57kUf0BryiR77FN9HA==
+MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEfIBFTz9lAkUblftBBD5WBY0fa8Lm
+rZZIENzLbQzn68tp2cuQre7NUhCmU/lG4QpQxADSBTRhHlXBVTbDWQtPxg==
 -----END PUBLIC KEY-----