fix(weights): guard DI_values None and read label_frequency_candles from freqai_info

fix(weights): guard DI_values None and read label_frequency_candles from freqai_info

- fit_live_predictions: pred_df.get('DI_values') returns None when
  feature_parameters.DI_threshold is 0 or absent (the default), causing
  AttributeError on the subsequent .mean()/.std() calls. Fall back to
  zeros instead.
- _label_frequency_candles: read from self.freqai_info['feature_parameters']
  (matching every other access in the file) instead of self.config, which
  is the top-level config dict and never contains feature_parameters
  directly. The previous code silently ignored user-provided values and
  always fell back to the default 'max(2, 2 * len(self.pairs))'.