feat: add Chapter 10 formalization on Hilbert’s third problem

[AItoBit]

Adds a single Lean 4 file covering results from Chapter 10 of Proofs from THE BOOK.

Includes:

• Cone Lemma and Fourier–Motzkin elimination.
• Pearl Lemma and Bricard’s condition.
• Dihedral-angle calculations and tetrahedron examples.
• Geometric decomposition definitions and polytope results.
• Minkowski–Weyl characterization of convex polytopes.

The Hilbert’s third problem result uses an abstract segment-and-angle decomposition model. Geometric equidecomposability is defined separately; the file does not establish the bridge from arbitrary geometric decompositions to this model.

Validation: the complete file compiles with zero errors and zero warnings using Lean 4.35.0-rc3 and Mathlib commit 738e62b. No sorry, admit, added axioms, unsafe declarations, or native_decide.