feat: add Base USDC and Agent Wallet payments

[boboliu-1010]

Summary

• add Base mainnet and Base Sepolia USDC support while keeping Agent Wallet as the default signer
• make registered token decimals authoritative and validate selected x402 requirements before dry-run or signing
• prevent signed payment requests from following redirects and leaking PAYMENT-SIGNATURE to another origin
• use chain-aware address comparison for EVM and TRON assets
• expose stable wallet/input error codes, canonical command identities, and single-document JSON output for roundtrip
• fix gateway catalog search parsing, repeatable inline headers, and command-specific help
• document Base payment, custom assets, redirect behavior, and Gateway/Catalog usage

Validation

• npm test — 35/35 passed
• npm run test:package — packed CLI 1.0.2-beta.1 verified
• npm ls --all --depth=1 — passed
• npm audit --omit=dev --audit-level=high — 0 vulnerabilities
• git diff --check — passed
• Base Sepolia payment was also validated against the deployed test environment