Add theory documentation for bits and qubits notebook

[Copilot]

Created 02_teoria_bits_y_cubits.md to document the theoretical foundations from the "02. Bits y Cúbits.ipynb" notebook.

Content Structure

• Classical bits and gates: Vector representation, tensor products, reversible computation (Landauer's Principle, CNOT/Toffoli gates)
• Qubits: State vectors with complex amplitudes, Bloch sphere parametrization (θ, φ), computational/X/Y bases, global vs relative phase
• Quantum gates: Pauli matrices (X, Y, Z), Hadamard, rotation operators (Rₓ, Rᵧ, R_z), Walsh-Hadamard transform
• Measurement: Postulate, observables as Hermitian operators, Pauli decomposition, expected values

Includes mathematical formulations and Qiskit implementation examples:

# State creation and visualization
estado = Statevector([a0, a1])
plot_bloch_multivector(estado)

# Observable definition
M = SparsePauliOp.from_list([
    ("XIX", 0.5),
    ("IYZ", -3),
    ("XXX", 2)
])

Document maintains Spanish language consistency with the source notebook and uses standard quantum mechanics notation (bra-ket, ⊗ for tensor products).

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[mateofra]

Primera vez que uso un agente, supongo que funciona. 😑