[0.98a4] PyClical Demo Refactoring & Test Harness Optimization

Description

This issue tracks the scope for GluCat release 0.98a4.

Release 0.98a4 establishes a dedicated PyClical Demos Sandbox, investigates Marimo reactive notebook integration alongside Jupyter, removes the legacy Mayavi 3D plotting backend in favor of PyVista, and optimizes test-one-config-option.sh and fast-test-one-config-option.sh to prioritize early failure detection via test_doctest.

Tasks & Checklist

1. Release Milestone Shift (TODO.md)

• Shift future 0.98a* release milestones in TODO.md to introduce 0.98a4:
  • 0.98a3: Defence in Depth & Quality Hardening (Current Release)
  • 0.98a4 (New): PyClical Demos Sandbox, Marimo Investigation & Test Harness Optimization
  • 0.98a5 (was 0.98a4): Raytracer
  • 0.98a6 (was 0.98a5): Documentation
  • 0.98a7 (was 0.98a6): Packaging

2. PyClical Demos Sandbox Reorganization (pyclical/demos/sandbox/)

• Create pyclical/demos/sandbox/ subdirectory.
• Move all text/numerical interactive tutorial and presentation scripts into sandbox/:
  • pyclical_tutorial_0_0_notation.py through pyclical_tutorial_1_5_conformal.py and pyclical_tutorial_2_0_wedge_product.py
  • clifford_demo.py, m_theory_demo.py, sqrt_log_demo.py, versor_demo.py, pyclical_demo.py, pyclical_tutorials.py
• Move runtime engine, build, and validation scripts into sandbox/:
  • pyclical_tutorial_utils.py, pyclical_notebook_utils.py, build_pyclical_notebooks.py, validate_notebooks.py, and .ipynb files
• Create pyclical/demos/sandbox/images/ and store local offline copies of Hermann_Graßmann.jpg and Clifford_William_Kingdon.jpg. Update clifford_demo.py to use relative local paths.
• Update pyclical/demos/Makefile.am and build rules to reflect the sandbox/ and plotting/ structure.

3. Marimo Notebook Integration Investigation

• Investigate generating reactive Marimo Python notebooks (.py) alongside Jupyter notebooks (.ipynb).
• Evaluate build_pyclical_notebooks.py and pyclical_notebook_utils.py extensions for dual notebook output generation and execution validation.

4. Mayavi Deprecation & Removal

• Remove legacy Mayavi scripts (plotting_demo_mayavi.py, setup-mayavi-env.sh, mayavi-env.yml, export-mayavi-vars.sh).
• Update pyclical/demos/plotting/Makefile.am to remove Mayavi dependencies, leaving PyVista as the single 3D plotting backend.

5. Test Harness Optimization

• Update test/test-one-config-option.sh to build and run test_doctest (make ${args} -C test_doctest check) before running the full test suite (make ${args} check).
• Update test/fast-test-one-config-option.sh to only build and run test_doctest (make ${args} -C test_doctest check).

Acceptance Criteria

• ./test/fast-test-one-config-option.sh and ./test/test-one-config-option.sh execute cleanly with test_doctest prioritization.
• cd pyclical/demos/sandbox && python3 build_pyclical_notebooks.py builds all notebooks and loads offline images without network calls or errors.
• make check and make check-python pass with 100% success across the reorganized repository structure.