Add async ICLabel browser execution

[neuromechanist]

Summary

• Add iclabel_async and pop_iclabel_async for Emscripten/Pyodide execution, with clear synchronous fail-fast errors.
• Add the ONNX Runtime Web bridge, Pyodide runner integration, async console and GUI session coordination, and stale-result protection.
• Add native-vs-browser parity tooling, CI coverage, user help, API docs, and workflow documentation.

Validation

• Focused tests: 26 passed, 2 skipped (MATLAB/PyTorch optional).
• Native/browser sample parity: allclose: true, shape [32, 7], max absolute difference 4.32133674621582e-06 at rtol=1e-4, atol=1e-5.
• ./pre-commit.py --changed-from origin/develop passed.
• Ruff, format, MJS syntax, and diff checks passed.

Fixes #378

[claude]

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[claude]

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