ENH: Add multi-object VTK→USD workflow and Greedy image registration

  - Add WorkflowConvertVTKToUSD for converting multi-object VTK scenes to
    animated USD with per-anatomy material assignment and colormap overlays
  - Add CLI command convert_vtk_to_usd for batch/scripted VTK→USD conversion
  - Add RegisterImagesGreedy wrapping the Greedy deformable registration tool
    as an alternative to ANTs/ICON; includes tests
  - Extend vtk_to_usd subpackage with mesh_utils (split by type/connectivity,
    colormap allocation) and enhance converter and data_structures
  - Enhance USDTools and USDAnatomyTools for multi-label anatomy and
    time-varying data preservation
  - Add CHOP Alterra valve and TPV25 valve USD conversion notebooks

Author: aylward

.pre-commit-config.yaml

@@ -27,6 +27,16 @@ repos:
         pass_filenames: false
         files: ^src/
 
+  # Strip notebook outputs and widget state when notebooks are committed
+  - repo: local
+    hooks:
+      - id: prepare-notebooks-for-commit
+        name: Prepare notebooks for commit (strip outputs and widget state)
+        entry: python utils/prepare_notebooks_for_commit.py
+        language: system
+        pass_filenames: false
+        files: \.ipynb$
+
   # Local tests (optional - can be disabled if too slow)
   - repo: local
     hooks:

README.md

@@ -560,6 +560,7 @@ pytest tests/ -m "not slow and not requires_data" -v
 pytest tests/test_usd_merge.py -v                           # USD merge functionality
 pytest tests/test_usd_time_preservation.py -v               # Time-varying data preservation
 pytest tests/test_register_images_ants.py -v                # ANTs registration
+pytest tests/test_register_images_greedy.py -v             # Greedy registration
 pytest tests/test_register_images_icon.py -v                # Icon registration
 pytest tests/test_register_time_series_images.py -v         # Time series registration
 pytest tests/test_segment_chest_total_segmentator.py -v     # TotalSegmentator

docs/developer/architecture.rst

@@ -59,6 +59,7 @@ The package is organized into functional modules:
    │   ├── Image Registration
    │   │   ├── register_images_base.py            Base registration
    │   │   ├── register_images_ants.py            ANTs registration
+   │   │   ├── register_images_greedy.py          Greedy registration
    │   │   ├── register_images_icon.py            ICON registration
    │   │   └── register_time_series_images.py     Time series
    │   │

docs/testing.rst

@@ -71,6 +71,7 @@ Specific Test Modules
 
    # Registration (slow, ~5-10 minutes each)
    pytest tests/test_register_images_ants.py -v
+   pytest tests/test_register_images_greedy.py -v
    pytest tests/test_register_images_icon.py -v
    pytest tests/test_register_time_series_images.py -v
 
@@ -107,6 +108,7 @@ Tests are organized by functionality:
    │
    ├── Registration Tests (Slow ~5-10 min)
    │   ├── test_register_images_ants.py          # ANTs registration
+   │   ├── test_register_images_greedy.py        # Greedy registration
    │   ├── test_register_images_icon.py          # Icon registration  
    │   └── test_register_time_series_images.py   # Time series registration
    │