Feature Request: Add autonomous wallet creation (createWallet)

## Summary
AI agents often need to create new wallets on the fly — without an existing funded account. This is useful for:

- **Multi-agent systems** where each agent spawns its own wallet
- **Autonomous sub-accounts** created programmatically
- **Testing/dev workflows** needing disposable wallets

## Proposed Feature

Add a `createWallet()` function that generates a fresh keypair:

```javascript
import { createWallet } from 'hedera-agent-kit';

const wallet = createWallet();
console.log(wallet.accountId); // Derived from public key
console.log(wallet.publicKey);
console.log(wallet.privateKey);
```

## Reference Implementation

I've published a lightweight implementation at [@aite550659/hedera-agent-wallet](https://www.npmjs.com/package/@aite550659/hedera-agent-wallet) (9 KB, 1 dependency).

Happy to contribute a PR if this would be valuable for the official kit.

## Use Case: Agent Trust Protocol (ATP)

We're building [ATP](https://medium.com/@TExplorer59/ai-agents-need-a-soul-and-it-should-be-immutable-fa06428d1ca1) — a protocol for AI agent ownership and trust on Hedera. Autonomous wallet creation is essential for agents that need economic agency without human intervention for each wallet.

cc @piotrswierzy @jaycoolh