Fix Ajv import compatibility issue by downgrading to v6

Downgrade Ajv from v8.17.1 to v6.12.6 to resolve ESM/CJS module compatibility issues that were causing "does not provide an export named 'Ajv'" errors in projects using this SDK. This ensures consistent import patterns across different module systems.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -46,7 +46,7 @@
     "client": "tsx src/cli.ts client"
   },
   "dependencies": {
-    "ajv": "^8.17.1",
+    "ajv": "^6.12.6",
     "content-type": "^1.0.5",
     "cors": "^2.8.5",
     "cross-spawn": "^7.0.5",