[Zig] Add high-level AES-GCM API

[roninjin10]

Summary

Add high-level AES-GCM API in Zig to match TypeScript's user-friendly interface.

TS High-Level API

• generateKey - Generate random AES key
• importKey - Import key from bytes
• exportKey - Export key to bytes
• encrypt - Simple encrypt with auto nonce
• decrypt - Simple decrypt
• generateNonce - Generate random nonce
• deriveKey - Derive key from password (PBKDF2)

Current State

Zig has low-level functions only:

• encrypt128, decrypt128
• encrypt256, decrypt256

Users must manage nonces, key generation manually.

Goal

Provide both low-level (current) and high-level (new) APIs.

Note: Issue created by Claude AI assistant, not @roninjin10 or @fucory