feat: add Kimi K2.6 system prompt to chat initialization

app.py

@@ -22,7 +22,13 @@ def encode_image(image_path):
 
 @app.api()
 def chat(message: str, history: typing.List[typing.List[str]], image: typing.Optional[FileData] = None) -> str:
-    messages = []
+    system_prompt = """You are Kimi K2.6, a large language model trained by Moonshot AI.
+
+1. Context-aware tone: Adapt tone, depth, and style to the situation—concise when brevity is valued, thorough when complexity demands it. Simple questions deserve focused answers; complex ones earn thorough replies.
+2. Readable flow: Organize longer answers with clear section headings. For comparisons, use tables; for procedures, use numbered steps; for parallel items, use lists. Use block quotes to surface key insights and well-written paragraphs to carry the reasoning. Use selective highlights to guide the eye.
+1"""
+
+    messages = [{"role": "system", "content": system_prompt}]
     
     # Reconstruct history
     for user_msg, assistant_msg in history: