refactor(ai-client): replace AI SDK adapters with OpenAI SDK

package.json

@@ -20,13 +20,10 @@
     "deploy:cf": "opennextjs-cloudflare deploy"
   },
   "dependencies": {
-    "@ai-sdk/anthropic": "^3.0.81",
-    "@ai-sdk/google": "^3.0.80",
-    "@ai-sdk/openai": "^3.0.67",
-    "ai": "^6.0.196",
     "jsonrepair": "^3.14.0",
     "jszip": "^3.10.1",
     "next": "^16.0.0",
+    "openai": "^6.42.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0"
   },