fix: report direction probability as signal confidence

更新 README，切换数据源为 AkShare，统一请求字段为 symbol，优化缓存机制，新增性能日志

Include prediction result in cache endpoint response

Add optional ts_code filter to GET /api/v1/cache

Add result cache with A-share market-close TTL

Add batch prediction endpoint

Initial deployment: Kronos stock predictor REST API