fix: add AI_MAX_TOKENS environment variable to prevent response truncation

## Problem
AI responses were being truncated due to a hardcoded max_tokens limit of 2000,
causing JSON parsing failures. The error occurred when:
1. AI's thought process analysis was cut off mid-response
2. extractDecisions() incorrectly extracted MACD data arrays from the input prompt
3. Go failed to unmarshal numbers into Decision struct
Error message:
```
json: cannot unmarshal number into Go value of type decision.Decision
JSON内容: [-867.759, -937.406, -1020.435, ...]
```
## Solution
- Add MaxTokens field to mcp.Client struct
- Read AI_MAX_TOKENS from environment variable (default: 2000)
- Set AI_MAX_TOKENS=4000 in docker-compose.yml for production use
- This provides enough tokens for complete analysis with the 800-line trading strategy prompt
## Testing
- Verify environment variable is read correctly
- Confirm AI responses are no longer truncated
- Check decision logs for complete JSON output

docker-compose.yml

@@ -17,6 +17,7 @@ services:
       - /etc/localtime:/etc/localtime:ro  # Sync host time
     environment:
       - TZ=${NOFX_TIMEZONE:-Asia/Shanghai}  # Set timezone
+      - AI_MAX_TOKENS=4000  # AI响应的最大token数（默认2000，建议4000-8000）
     networks:
       - nofx-network
     healthcheck: