[ HumanjavaEnterprises/nostr-crypto-utils ] fix: NIP-04 encryption format to match specification

HIGH: encrypt/decrypt used non-standard hex format (iv + ciphertext
concatenated). Now uses NIP-04 standard: base64(ciphertext)?iv=base64(iv).

Decrypt supports legacy hex format as backwards-compatible fallback.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
https://github.com/HumanjavaEnterprises/nostr-crypto-utils/commit/d4574cdde7e551214280bb2f91b55504aff75dc4