Add PCA Component and Metrics Visualization Tab

[eurunuela]

Summary

Tedana outputs several PCA-related files (e.g., desc-PCA_metrics.tsv, desc-PCA_mixing.tsv, desc-PCA_stat-z_components.nii. gz) that contain important dimensionality reduction information prior to ICA decomposition. Rica currently lacks a dedicated PCA visualization.

Additional Detail

Add a "PCA" tab to Rica that displays:

• PCA scatter plots for metrics and explained variance
• Interactive visualization of PCA stat-z maps (using Niivue/mosaic, like ICA)
• Table of metrics and mixing coefficients with sort/filter options
• Option to compare PCA and ICA components side-by-side
• Documentation linking to tedana's PCA outputs

Next Steps

1. Design wireframe/UI for PCA tab
2. Identify standard PCA metrics in tedana outputs
3. Integrate Niivue-brain viewer for PCA maps
4. Implement table and scatter plot widgets
5. Update docs and onboarding for new tab