Switch to CDP facilitator with CAIP-2 network format

- Update default facilitator URL to Coinbase CDP
- Change network format from 'base' to CAIP-2 'eip155:8453'
- Add documentation for CDP credential requirements
- Fix network variable scope issue in x402.js

This enables auto-registration in the x402 Bazaar discovery layer
when the first payment is processed through the CDP facilitator.

.env-example

@@ -25,14 +25,24 @@ export PORT=5942
 export X402_ENABLED=true
 export SERVER_BASE_ADDRESS=0xd32585CE60815654C50CAf350e18de8096061e63
 export X402_PRICE_USDC=0.1
-export x402_NETWORK=base
-export x402_FACILITATOR_URL=http://localhost:4022
 
+# Network configuration (CAIP-2 format required by CDP)
+# Use 'eip155:8453' for Base mainnet
+# Use 'eip155:84532' for Base Sepolia (testnet)
+export x402_NETWORK=eip155:8453
+
+# Facilitator URL
+# For Coinbase CDP (recommended): https://api.cdp.coinbase.com/platform/v2/x402
+# For custom/local facilitator: http://localhost:4022
+export x402_FACILITATOR_URL=https://api.cdp.coinbase.com/platform/v2/x402
+
+# CDP API Credentials (required when using CDP facilitator)
+# Get these from https://cdp.coinbase.com - API Keys section
+export FACILITATOR_KEY_ID=your_key_id_here
+export FACILITATOR_SECRET_KEY=your_secret_key_here
 
 # Basic Authentication required to access this API?
 export USE_BASIC_AUTH=true
 export BASIC_AUTH_TOKEN=some-random-token
 
 # END ACCESS CONTROL
-
-npm start