feat(editor): add Markdown rendering for ghost text and optimize prompt system

- Implement Markdown parsing for ghost text using Milkdown parser
- Add support for both block and inline content in ghost text
- Refactor prompt system with comprehensive rules and examples
- Adjust LLM parameters: increase temperature to 0.7, add repeat_penalty
- Add CSS styles for formatted ghost text (bold, italic, code, links)
- Add documentation for Copilot prompt system and ghost text rendering

backend/main.py

@@ -89,7 +89,6 @@ async def create_completion(request: CompletionRequest):
             messages=[{'role': 'user', 'content': prompt}],
             stream=False,
             options={
-                'num_predict': 8192,
                 'temperature': 0.2,
             }
         )