Sync chat template with v5_1 (matches base/FP8/INT4)

Brings NVFP4 in line with the other Laguna-XS.2 repos, which all ship the v5_1 template. Behavior delta: when callers do not provide a system message, the default Poolside assistant system message is now used (was empty).

chat_template.jinja

@@ -1,12 +1,12 @@
-{#- Copied from laguna_glm_thinking_v4/chat_template.jinja -#}
-{#- Removes prefix that references <think> token, and replaces message.reasoning_content reference with message.reasoning -#}
+{#- Iteration on laguna_glm_thinking_v5/chat_template.jinja -#}
+{#- Adds a default system message (used when no system message is provided in `messages`). -#}
 {{- "〈|EOS|〉" -}}
 {%- set enable_thinking = enable_thinking | default(false) -%}
 {%- set render_assistant_messages_raw = render_assistant_messages_raw | default(false) -%}
 {%- set add_generation_prompt = add_generation_prompt | default(false) -%}
 
 {#- ───── header (system message) ───── -#}
-{%- set system_message = "" -%}
+{%- set system_message = "You are a helpful, conversationally-fluent assistant made by Poolside. You are here to be helpful to users through natural language conversations." -%}
 {%- if messages and messages[0].role == "system" -%}
   {%- set system_message = messages[0].content -%}
 {%- endif -%}