Sync into sphinx branch after Sept 2025 sprint

[ashwinvis]

• add missing import to pandas (if downloading data from zenodo)
• add missing import
• fix bulleted list formatting
• Add diagonal ref. line to plot_predictions() function and update figs on lesson page
• [actions] update sandpaper workflow to version 0.16.12 (Update Workflows to Version 0.16.12 carpentries-lab/deep-learning-intro#581)
• Fixed some dead links (Fix links carpentries-lab/deep-learning-intro#590) (Fixed some dead links (#590) carpentries-lab/deep-learning-intro#591)
• Fix Carpentries incubator links to lab.
• Fix link to local repository.
• Clean up maintainer list.
• deleted the line that fixes numpy seed, since according to docs, it is redundant with the keras set_random_seed
• added keras.utils.set_random_seed(2) to apisodes 3,4,5
• Change colormap of confustion matrix to Blues
• Fix plot y axis label.
• create_nn() now takes the input shape as an argument
• Remove wrong y axis label.
• expand alt text descriptions
• expand alt text descriptions
• Update training curve plot.
• fix challenge-solution format
• Add alt text for updated plot.
• fix typos and address inaccuracy
• improve alt text description
• minor polish for clarity
• correct image dimensions
• add Dive into Deep Learning to list of resources
• added clarification comment about None value in params
• Harmonize link, remove dead link.
• Add config and Github action for Linkspector.
• Clarify the solution which describes the need for a test set
• Add Callout about metrics. (Add Callout about metrics. carpentries-lab/deep-learning-intro#607)
• Demystify the number of parameters in Conv2D layers

[github-actions]

⚠️ WARNING ⚠️

This pull request contains a mix of workflow files and regular files. This could be malicious. No preview will be created.

regular files:

• .linkspector.yml
• CODE_OF_CONDUCT.md
• CONTRIBUTING.md
• README.md
• episodes/1-introduction.md
• episodes/2-keras.md
• episodes/3-monitor-the-model.md
• episodes/4-advanced-layer-types.md
• episodes/5-transfer-learning.md
• episodes/6-outlook.md
• episodes/fig/02_training_curve.png
• episodes/fig/03_regression_predictions_testset.png
• episodes/fig/03_regression_predictions_trainset.png
• episodes/fig/03_regression_test_5_dropout_batchnorm.png
• episodes/fig/03_regression_test_5_naive_baseline.png
• episodes/fig/03_scatter_plot_basel_model.png
• episodes/fig/03_training_history_1_rmse.png
• episodes/fig/03_training_history_5_rmse_batchnorm.png
• episodes/fig/confusion_matrix.png
• instructors/bonus-material.md
• instructors/instructor-notes.md
• learners/reference.md
• learners/setup.md
• paper/paper.md

workflow files:

• .github/workflows/README.md
• .github/workflows/linkspector.yml
• .github/workflows/sandpaper-version.txt