Add EIP-8004 agent registration tutorial

[hammertoe]

Summary

This PR adds a comprehensive tutorial demonstrating how to register an ERC-8004 compliant autonomous agent with
verifiable persistent storage using Filecoin Pin.

What's Added

New Tutorial: TUTORIAL.md - Complete guide for registering ERC-8004 agents with Filecoin storage

The tutorial walks developers through:

1. Creating an ERC-8004 compliant agent card (JSON metadata)
2. Uploading to Filecoin Pin with cryptographic PDP (Proof of Data Possession) proofs
3. Registering the agent on-chain as an NFT on Base Sepolia
4. Verifying storage persistence and on-chain registration

Why This Matters

The Problem: ERC-8004 agents need persistent storage for their metadata (agent cards). Generic IPFS pinning
services can stop hosting data without notice, and centralized storage creates single points of failure.

The Solution: Filecoin Pin provides cryptographically-verified persistent storage with daily PDP proofs, ensuring
agent metadata remains available and verifiable long-term.

Tutorial Highlights

• ✅ Follows official Filecoin docs style - Matches structure and tone of existing Filecoin Pin CLI tutorial
• ✅ Complete prerequisites - Links to wallet setup, includes Base Sepolia ETH faucet, lists all required tokens
• ✅ Real-world example - Demonstrates GitHub Integration Agent using GitHub's actual public MCP server
• ✅ Step-by-step instructions - Clear bash commands with expected outputs
• ✅ Screenshot indicators - Placeholders showing what visuals to add
• ✅ Troubleshooting section - Common issues and solutions
• ✅ What's Next - Guides builders on next steps

Target Audience

• ERC-8004 agent builders needing persistent storage
• Developers exploring trustless autonomous agents
• Projects requiring verifiable decentralized storage

Technical Details

Networks Used:

• Filecoin Calibration testnet (storage with PDP proofs)
• Base Sepolia testnet (ERC-8004 Identity Registry)

Key Technologies:

• Filecoin Pin CLI
• Foundry (cast command)
• ERC-8004 standard
• IPFS/CID addressing

Testing

Tutorial has been tested end-to-end with:

• Agent card uploaded to Filecoin Pin (CID: bafybeihhal5hlbylkibniig6j72wdrm7lr4nf6z47natleh2jkyosrg7di)
• Agent registered on Base Sepolia (Agent ID: 55)
• PDP proofs verified and active
• IPFS retrieval confirmed working