docs(Electromagnetism): document the three-dimensional Maxwell equations module

[sankalpsthakur]

Documents the three-dimensional Maxwell equations module: lists the four results it proves (gaussLawElectric, gaussLawMagnetic, ampereLaw, faradayLaw), explains how they relate to the covariant IsExtrema formulation (the two inhomogeneous equations come from the extremality condition, the two homogeneous ones follow directly from the potential definitions), and notes the current scope (pointwise differential form in free space; integral formulations, boundary conditions, and material media are out of scope).

Documentation only — no declarations, proofs, or signatures changed.

AI/LLM disclosure

AI coding tools were used to help draft this documentation. I reviewed the complete change for accuracy before submitting.

[github-actions]

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[gloges]

Looks good - I've left one minor suggested rephrasing for referring to Gauss's law.

[gloges]

@sankalpsthakur the linters are failing because the changed lines are now too long - 100 char max! When ready you can comment with "-awaiting-author" to remove the tag (this helps reviewers keep track of the PR's status).

[sankalpsthakur]

-awaiting-author

Changed lines wrapped to the 100-char limit and the Gauss's-law wording is in; all four linter jobs are green. Thanks @gloges!

[gloges]

Great - thanks again!