feat: implement inline autocomplete suggestions with FastAPI backend and Milkdown editor integration

backend/prompt.py

@@ -0,0 +1,28 @@
+import os
+from typing import Tuple
+
+def build_prompt(prefix: str, suffix: str) -> str:
+    """
+    构建用于代码补全的 Prompt。
+    参考 completions-sample-code 的 extractPrompt 逻辑简化实现。
+    """
+    MAX_CONTEXT_LINES = 30
+    
+    prefix_lines = prefix.split('\n')
+    suffix_lines = suffix.split('\n') if suffix else []
+    
+    recent_prefix = '\n'.join(prefix_lines[-MAX_CONTEXT_LINES:])
+    recent_suffix = '\n'.join(suffix_lines[:5])
+
+    prompt = f"""
+You are a helpful writing assistant. Continue the text naturally based on the context.
+
+Context (before cursor):
+{recent_prefix}
+
+Complete this:
+{suffix if suffix else '(cursor here)'}
+
+Continue:"""
+    
+    return prompt.strip()