feat: add angular momentum squared and ladder operators

[lizr-phys]

This extends the angular-momentum operators from #1673 on the common invariant Schwartz domain. It transports the existing Schwartz-space 𝐋² to a densely defined Hilbert-space operator, proves its component-sum formula and symmetry, and identifies the right-handed 3D components Lx = L₁₂, Ly = L₂₀, Lz = L₀₁. The Schwartz and Hilbert-space APIs then establish the Levi-Civita/cyclic commutation relations and the identities [Lz,L±] = ±ℏ L± and [L²,L±] = 0. Hilbert-space commutators are stated pointwise on Schwartz vectors with membership proofs for intermediate applications. No new dependency is added.

Reviewer map: Start with the angularMomentumSqOperator additions in AngularMomentum.lean, then read ThreeDimensional.lean in order: Cartesian components, commutation algebra, ladder operators. API-map.yaml and Physlib.lean record the API and new import.

Local validation: On the latest upstream/master, Lake rebuilt both changed angular-momentum modules and their hydrogen downstream module. Focused Lean linters (15 checks on both modules), axiom audit, import check, API-map check, style check, codespell, and git diff --check passed. On this Windows machine, lake --no-cache exe lint_all cannot start its native C dependencies because cc is unavailable.

AI assistance: Codex (GPT-6 Astra).

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[jstoobysmith]

Added one comment here, but there are also a couple of comments on the Lean Zulip, which should be discussed.

[jstoobysmith]

I wouldn't define this, maybe we just come up with a notation for a general QuantumMechanics.angularMomentum3DOperator i?

[jstoobysmith]

awaiting-author