Add WMA-based hemisphere export mode

[guikunchen]

Summary

This PR adds a Hemisphere export mode to the TractCloud CLI.

When --hemisphere-atlas-dir is provided, TractCloud now:

• runs normal fine-cluster inference
• registers the input tractography to the ORG atlas using WMA
• assigns streamlines to left, right, or commissural groups
• writes hemisphere-split .vtp tract files
• writes an annotated whole-tractography file with FineLabel, CoarseID, and HemisphereLocation cell arrays
• writes a hemisphere_summary.json

Default CLI behavior is unchanged when --hemisphere-atlas-dir is omitted. Hemisphere mode does not support --mrb and does not export Other tract bundles.

Changes

• Added src/tractcloud/hemisphere.py
• Added --hemisphere-atlas-dir CLI option
• Refactored pipeline inference so hemisphere mode can reuse raw fine-cluster predictions
• Added WMA as a Git dependency:
  whitematteranalysis @ git+https://github.com/SlicerDMRI/whitematteranalysis.git
• Added Hemisphere mode documentation in src/tractcloud/README_hemisphere.md

[ljod]

I looked with Guikun and results look correct after running this, and it solves a big user issue. Hoping Steve @pieper can take a quick look at this too

[pieper]

Sounds good to me 👍