Add MerchantGuard to ecosystem directory (x402-foundation#1160)

AI-powered compliance infrastructure for the agent economy with
three x402-gated API products on Base mainnet (USDC):

- GuardScore: Merchant risk scoring API ($0.10/call)
- GuardScan: 3-layer security scanner (100 patterns)
- Mystery Shopper: 10-probe agent certification

Live at https://www.merchantguard.ai

Co-authored-by: MerchantGuardOps <194741315+MerchantGuardOps@users.noreply.github.com>

Author: MerchantGuardOps

typescript/site/app/ecosystem/partners-data/merchantguard/metadata.json

@@ -0,0 +1,7 @@
+{
+  "name": "MerchantGuard",
+  "description": "AI-powered compliance infrastructure for the agent economy. x402-gated APIs: GuardScore (merchant risk scoring), GuardScan (3-layer security scanner), and Mystery Shopper (10-probe agent certification). USDC on Base.",
+  "logoUrl": "/logos/merchantguard.png",
+  "websiteUrl": "https://www.merchantguard.ai",
+  "category": "Services/Endpoints"
+}