Consistent 5D Kaluza-Klein Unification with Quantum-Stabilised Vacuum and Positive Cosmological Constant

We derive a self-consistent five-dimensional Kaluza-Klein theory in which the compactification radius is stabilised by the interplay between the one-loop Casimir energy of bulk fields
and a topologically quantised 4-brane tension. The dimensional reduction is carried out with
full control of all conformal factors, yielding the correct Einstein-frame dilaton-Maxwell coupling and a canonically normalised radion. The total effective potential possesses a nontrivial minimum; a constant uplift term is then tuned to produce the tiny observed positive
cosmological constant. The dilaton acquires a large mass, evading fifth-force bounds, and
the low-energy limit is exactly Einstein-Maxwell theory.