feat(QuantumMechanics/Hydrogen): prove angularMomentum_commutation_lrl

[TomOleDiem]

Closes the `@[sorryful]` gap on `HydrogenAtom.angularMomentum_commutation_lrl`
(`⁅𝐋ᵢⱼ, 𝐀(ε)ₖ⁆ = iℏ(δᵢₖ𝐀(ε)ⱼ - δⱼₖ𝐀(ε)ᵢ)`, the regularized Laplace–Runge–Lenz vector
transforming as a vector under rotations), using only already-proved companion
commutators from Operators/Commutation.lean (angularMomentum_commutation_angularMomentum,
_momentum, _radiusRegPow, _position) and lrlOperator_eq''s expanded form of 𝐀(ε)ᵢ.

Adds one private helper, angularMomentum_commutation_Ldot_p, for how 𝐋ᵢⱼ commutes
with the 𝐋ₖ⬝ᵥ𝐩 term in that expansion.

angularMomentum_commutation_lrlSqr and angularMomentumSqr_commutation_lrlSqr were
already fully proved modulo this one dependency, so their @[sorryful] tags come off
too — #print axioms on all three now shows only propext/Classical.choice/
Quot.sound, matching sorryfulPseudoTest's "tagged sorryful iff it actually contains
sorryAx" invariant. Whole-library lake build Physlib is clean.

One file changed, 27 lines.

---

Related: #991 attempted the same fix, but predates the package's rename/reorg (it's
against the old PhysLean/QuantumMechanics/DDimensions/... path, before the current
flat Physlib/QuantumMechanics/... layout) and hasn't had activity since April, so it
no longer applies against current master. If this one looks good to you, might be
worth closing #991 in favor of it — entirely your call, just flagging the overlap.

🤖 Generated with Claude Code

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[jstoobysmith]

Looks like a great first PR. Just one comment from me here. Many thanks.

[jstoobysmith]

Probably doesn't need to be a private lemma.

[jstoobysmith]

awaiting-author

[nateabr]

Hi @TomOleDiem, when you're ready for your PR to be reviewed again please comment:

-awaiting-author

[nateabr]

Have done it for you this time :)

Thanks for your PR