docs: new algorithm migration guides + memory evaluation (#4811)

Co-authored-by: kartik-mem0 <kartik.labhshetwar@mem0.ai>
Co-authored-by: Saket Aryan <saketaryan2002@gmail.com>

docs/integrations/llama-index.mdx

@@ -83,7 +83,7 @@ config = {
     "llm": {
         "provider": "openai",
         "config": {
-            "model": "gpt-4.1-nano-2025-04-14",
+            "model": "gpt-5-mini",
             "temperature": 0.2,
             "max_tokens": 2000,
         },
@@ -116,7 +116,7 @@ from dotenv import load_dotenv
 load_dotenv()
 
 # os.environ["OPENAI_API_KEY"] = "<your-openai-api-key>"
-llm = OpenAI(model="gpt-4.1-nano-2025-04-14")
+llm = OpenAI(model="gpt-5-mini")
 ```
 
 ### SimpleChatEngine