Add CLAUDE.md for Claude Code onboarding

[waltsims]

Provides build/test commands, architecture overview, and project-specific naming conventions so future Claude Code sessions can be productive immediately.

Greptile Summary

This PR adds a CLAUDE.md onboarding file to help Claude Code sessions hit the ground running with correct build/test commands, a clear architecture overview, and project-specific naming conventions.

The document is well-structured and largely accurate — the architecture descriptions, backend dispatch logic, core data-class references, utility module listing, and naming conventions all match the implementation. Two small inaccuracies in the Testing section are worth fixing before merging:

• The KWAVE_MATLAB_REF_DIR env var is not used by the @pytest.mark.integration test suite (which uses a hardcoded collectedValues/ path); it is only an optional override for test_example_parity.py.
• assert_fields_close is described as a "fixture" but it is a plain helper function; only load_matlab_ref carries the @pytest.fixture decorator.

Confidence Score: 5/5

Safe to merge; documentation-only change with no runtime impact.

All findings are P2 — minor documentation inaccuracies in the Testing section. No code is changed, so there is zero risk of runtime regression. The inaccuracies could mislead a future Claude session but do not block merge.

CLAUDE.md (Testing section, lines 86–87)

Important Files Changed

Filename	Overview
CLAUDE.md	New onboarding guide for Claude Code; mostly accurate but contains two inaccuracies — wrong env-var description for integration test data, and assert_fields_close is mislabelled as a fixture.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["kspaceFirstOrder(kgrid, medium, source, sensor)"] --> B{pml_size == 'auto'?}
    B -- yes --> C[get_optimal_pml_size]
    B -- no --> D{pml_inside == False?}
    C --> D
    D -- yes --> E[_expand_for_pml_outside]
    D -- no --> F{backend?}
    E --> F
    F -- python --> G["Simulation (kspace_solver.py)\nNumPy / CuPy"]
    F -- cpp --> H["CppSimulation (cpp_simulation.py)\nHDF5 → C++ binary → HDF5"]
    G --> I{pml_inside == False?}
    H --> J{save_only?}
    J -- yes --> K[Return input/output file paths]
    J -- no --> I
    I -- yes --> L[_strip_pml]
    I -- no --> M[Return result dict]
    L --> M

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.40%. Comparing base (9201dea) to head (c954733).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #696   +/-   ##
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  Coverage   74.40%   74.40%           
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  Files          56       56           
  Lines        8026     8026           
  Branches     1570     1570           
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  Hits         5972     5972           
  Misses       1437     1437           
  Partials      617      617           

Flag	Coverage Δ
3.10	74.40% <ø> (ø)
3.11	74.40% <ø> (ø)
3.12	74.40% <ø> (ø)
3.13	74.40% <ø> (ø)
macos-latest	74.38% <ø> (ø)
ubuntu-latest	74.38% <ø> (ø)
windows-latest	74.39% <ø> (ø)

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