First implementation (#1)

Reviewed-on: #1

fixtures/packages/hale2026harmonic-damb/derived/mathml.jsonl

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+{"mathml":"<math display=\"block\"><msub><mi>E</mi><mtext>bond</mtext></msub><mo>=</mo><mfrac><mn>1</mn><mn>2</mn></mfrac><msub><mi>K</mi><mi>r</mi></msub><msup><mrow><mo>(</mo><mi>r</mi><mo>−</mo><msub><mi>r</mi><mtext>eq</mtext></msub><mo>)</mo></mrow><mn>2</mn></msup></math>","node":"tkxsmts","run":null,"tool":{"name":"hand","version":"0"}}