[Examples] Upgrade miscellaneous dependencies (#809)

Author: akaashrp

examples/embeddings/package.json

@@ -16,6 +16,6 @@
   },
   "dependencies": {
     "@mlc-ai/web-llm": "^0.2.82",
-    "langchain": "0.2.15"
+    "langchain": "^0.3.37"
   }
 }

examples/next-simple-chat/package.json

@@ -17,7 +17,7 @@
     "eslint": "8.44.0",
     "eslint-config-next": "13.4.7",
     "next": "^16.2.2",
-    "postcss": "8.4.24",
+    "postcss": "^8.4.31",
     "react": "18.2.0",
     "react-dom": "18.2.0",
     "tailwindcss": "3.3.2",