feat(PhyslibAlpha): characterize equality in state uncertainty relations

[naype888-cloud]

Summary

• Add the nonnegative centeredGramDefect to the algebraic uncertainty framework
• Characterize equality in Robertson and Robertson–Schrödinger: the uncertainty product saturates iff the centered Gram defect vanishes
• Five new lemmas completing the equality direction of the state uncertainty API

Continues the chain from PR #1587 (mixed-state Robertson).

Context

Part of the Nava–Robertson pillar series formalizing the Gram → Cauchy–Schwarz → Robertson → Fiedler → Niven → Szegő chain in PhysLean's algebraic framework.

Test plan

• CI passes (Build, Lint, imports check)
• No sorry, no new axioms beyond standard

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[github-actions]

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[jstoobysmith]

Approved.