Harden motor database release pipeline

[SiboVG]

Makes the database release process safer:

• Separates building, signing, and publishing
• Keeps the signing key isolated
• Pins GitHub Actions to commit SHAs, so the workflow always runs the exact reviewed code even if a version tag is later moved or compromised.
• Validates database integrity, counts, hashes, and signatures before publishing
• Uses OpenSSL for signing instead of Python cryptography dependencies