improve model identity in chat template

chat_template.jinja

@@ -30,7 +30,7 @@
         {{- visible_text(system_message.content) }}
     {%- else -%}
         {%- if model_identity is not defined -%}
-            {%- set model_identity = "You are a helpful assistant." -%}
+            {%- set model_identity = "You are MiniMax-M2, a helpful AI assistant built by MiniMax. Knowledge cutoff: 2025-06." -%}
         {%- endif -%}
         {{- model_identity }}
     {%- endif -%}