wallet: raw private key import.

private key import

raw secp256k1 private keys (64 hex characters) can now be imported through the wallet modal. the same AES-256-GCM encryption with PBKDF2 (1M iterations) protects both mnemonic and private key accounts.

security audit passed. 0 critical, 0 high findings. see cyber/security audit private key import.

unlock bar

private-key accounts show the password unlock bar. previously showed "choose account in your wallet" with no way to unlock.

applied across branches

cherry-picked to all 8 active branches.