- Replace fmt.Appendf with json.Marshal for structured log output
- Add logData map with level/type/method/path/query/response_time/status/user_agent/ip/timestamp fields
- Update logSlowRequest to output JSON-formatted logs with newline terminator for better log parsing and monitoring integration
- Add ResponseWriterWrapper struct with gin.ResponseWriter and body buffer fields to capture response content
- Add Write method to ResponseWriterWrapper that captures response body while writing to original writer
- Add Body method to ResponseWriterWrapper that returns captured response bytes
- Update ContentBasedETagMiddleware to wrap response writer with ResponseWriterWrapper before calling