feat: add Etherlink x402 support + non-custodial agent section

- Add Etherlink to supported chains (x402 went live on Etherlink March 2026)
- Update x402 section to mention Base + Etherlink multichain support
- Add 'Why Non-Custodial Matters for Agents' section (3 bullet points)
  vs OKX OnchainOS and other exchange-based agent wallets
- Expand 'Why Non-Custodial Beats Exchange Wallets' competitive section

Author: Max

README.md

@@ -190,6 +190,7 @@ for (const entry of history) {
 | **Ethereum** | ✅ | High-value operations |
 | **Arbitrum** | ✅ | DeFi agents |
 | **Polygon** | ✅ | Micropayments |
+| **Etherlink** | ✅ | x402 multichain payments |
 
 ## x402 Protocol Support
 
@@ -324,6 +325,14 @@ If you need a quick integration and you're already in the Coinbase ecosystem: th
 
 ---
 
+## Why Non-Custodial Matters for Agents
+
+Three reasons agents need non-custodial wallets, not exchange accounts:
+
+- **Agent-sovereign by design.** The agent's private key lives in its own environment -- not on OKX, not on Coinbase, not on anyone's server. No exchange can freeze it, no compliance team can lock it, no API deprecation can kill it.
+- **On-chain spend limits, not platform policies.** Custodial wallets enforce limits at the API layer. Those policies can change. This SDK enforces limits inside an EVM contract -- the chain enforces it, not a company.
+- **No exchange holds the keys.** When OKX OnchainOS or Coinbase Agentic Wallets hold your agent's key, they own the wallet. If they go down, if they get hacked, if they decide to shut down the product -- your agent stops working. Non-custodial means the wallet is yours as long as the chain runs.
+
 ## Why Non-Custodial Beats Exchange Wallets
 
 OKX OnchainOS supports 60+ chains. Coinbase Agentic Wallets are backed by a trillion-dollar exchange. Both look impressive on paper. Here's the problem: **they hold your agent's keys.**