Matrix basics

What this is? A self‑contained, browser‑only reproduction of five matrix calls:

• Matrix([[1, 3], [-2, 3]]) * Matrix([[0, 3], [0, 7]])
• Matrix([[1, 3], [-2, 3]]) ** 2
• Matrix([[1, 3], [-2, 3]]) ** -1 (2×2 inverse via adjugate/determinant)
• Matrix([[1, 0, 1], [2, -1, 3], [4, 3, 2]]).det() (Sarrus/Laplace)
• Matrix([[3, -2, 4, -2], [5, 3, -3, -2], [5, -2, 2, -2], [5, -2, -3, 3]]).eigenvals() (Faddeev–LeVerrier → characteristic polynomial → integer roots)

The harness then checks the answers with algebraic identities (e.g., Cayley–Hamilton, inverse correctness).