Adding enterpriseId as AES-GCM AAD to PRF-encrypted private keys

• Thus with ADD a ciphertext encrypted under a given enterprise has a cryptographic binding to that enterprise.
• Decryption is fully backward-compatible: decryptV2 reads adata from the envelope, old blobs (no adata) continue to decrypt normally, and no API signatures changed.

Note: what if no enterprise?

• attachPasskeyToWallet: safe, already throws before reaching encrypt if enterprise is missing

and

• wallets.ts wallet creation: params.enterprise is enterprise?: string (optional). undefined is handled
• wallets.ts bulk share accept: walletShare.enterprise is also optional. undefined is handled

so enterprise membership should already be enforced by the server first.

Ticket: WCN-1074