feat: switch from OpenAI API to native Ollama Python client

This commit refactors the LLM integration to use Ollama's native Python client instead of OpenAI-compatible API, while fixing critical template syntax errors and improving project structure.

Key changes:
- Replace openai package with ollama package in backend requirements
- Rewrite llm.py to use ollama.AsyncClient for direct Ollama API calls
- Update main.py to use non-streaming Ollama responses with thinking extraction
- Fix template syntax error in MilkdownEditor.vue (GhostTextOverlay component tags)
- Fix string截取错误 by using slice() instead of substring()
- Add src/utils/api.js and src/utils/config.js for shared configuration
- Add CORS middleware to FastAPI backend
- Update prompt.py with clearer instructions for continuation generation
- Add comprehensive README.md documentation

BREAKING CHANGE: Environment variables OLLAMA_BASE_URL changed to OLLAMA_HOST (remove /v1/ suffix)

backend/prompt.py

@@ -3,8 +3,8 @@ 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。
+    改进后的提示词构建函数。
+    使用更明确的指令来引导模型生成高质量的续写内容。
     """
     MAX_CONTEXT_LINES = 30
     
@@ -14,15 +14,21 @@ def build_prompt(prefix: str, suffix: str) -> str:
     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.
+    prompt = f"""You are an expert writing assistant. Continue the text naturally.
 
-Context (before cursor):
-{recent_prefix}
+CONTEXT:
+⟨CURSOR⟩ marks where to continue.
+- Before ⟨CURSOR⟩: existing text
+- After ⟨CURSOR⟩: following context (if any)
 
-Complete this:
-{suffix if suffix else '(cursor here)'}
+RULES:
+- Match existing style, tone, and terminology
+- Maintain logical flow
+- Write only the continuation, nothing else
 
-Continue:"""
+TEXT:
+{recent_prefix}⟨CURSOR⟩{recent_suffix}
+
+CONTINUATION:"""
     
     return prompt.strip()