Replaces placeholder ota_verify_signature_with_key with real mbedtls ECDSA verify; adds 4-case native test suite with generated P-256 vectors. Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>
Replaces placeholder ota_verify_signature_with_key with real mbedtls ECDSA verify; adds 4-case native test suite with generated P-256 vectors. Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>