Add auxiliary-task and annotator analyses for manuscript revision

[Caroline070590]

This pull request adds the auxiliary-task assessment used for the manuscript revision.

It includes:

• five matched-seed CalMS21 leave-one-task-out decoding pipelines;
• all-seed aggregation and figure-generation code;
• CalMS21 Task 2 and MARS1 annotator-agreement summaries;
• label-prevalence and bout-duration summary tables;
• code and final outputs for the combined six-panel annotator/bout figure;
• provenance and checksum documentation.

Raw annotations, pose data, embeddings, model weights, private paths, and unrelated exploratory analyses are excluded.

The original upstream script used to generate all annotator/bout summary tables from the raw annotations was not recovered. This limitation is documented explicitly; the preserved summary tables and final plotting workflow are included without reconstructing scientific results.