feat: Unify passphrase prompts for unlocking key

[samricotta]

Currently, operators must enter their passphrase twice when unlocking the key:

# First time
curl -X POST http://127.0.0.1:9791/v1/unlock -d '{"passphrase": "..."}'

# Second time (prompted again)

This creates unnecessary friction and potential for error. We should modify the unlock process to:

• Either accept the passphrase once via the /v1/unlock endpoint or use the additional prompt