Fix demo notebook inference flows and stride install docs

[Vedasheersh]

Summary

• update the single, batch, and Colab demo notebooks to use the maintained shared inference pipeline
• remove the old Colab pinned-commit / handwritten prediction flow in favor of the current pipeline
• clarify the README stride installation command and note that the kimlab::stride shorthand can fail on some conda setups

Issue coverage

• addresses the notebook/demo path behind Bug in def get_predictions(parameter, outfile): #19
• addresses the stride install clarification for kimlab::stride dependency is unavailable #32
• addresses the demo usability part of Problems with batch_demo.ipynb (batch_kcat_input_output.csv not generated) + fine-tuning #24
• updates the Colab notebook path discussed in Prediction failed #26

Validation

• jq empty batch_demo.ipynb single_demo.ipynb colab_demo.ipynb
• spot-checked notebook cells to confirm they call run_prediction_pipeline