chore: add repository field (required for npm provenance attestation)

Author: drewstone

package.json

@@ -2,6 +2,10 @@
   "name": "@tangle-network/agent-gateway",
   "version": "0.7.0",
   "packageManager": "pnpm@10.28.0",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/tangle-network/agent-gateway.git"
+  },
   "type": "module",
   "description": "x402 + API key payment gateway for Tangle agent products. Mount on any Hono app to expose agents as paid OpenAI-compatible endpoints.",
   "exports": {