Unified Fluctuation Geometry II Cosmological Background, Phase Organization, and the Unified Dark Sector

Following the foundational axioms established in Part I, this paper develops the cosmological background dynamics of Unified Fluctuation Geometry (UFG). We derive a modified FRW-type framework where large-scale expansion is governed not by independent dark components, but by the phase organization of a singular geometric sector. Within this description, "Dark Matter" and "Dark Energy" emerge as effective manifestations of contraction-like and expansion-like geometric modes. We demonstrate that the standard CDM model is recovered as a limiting regime, while the inherent Scale-Dependent Dimensionality (ε ~ 10^-5) provides a natural resolution to the Hubble Tension. By introducing a running geometric coupling and a phase transition mechanism at z ≈ 0. 338, UFG reconciles the discrepancy between CMB-derived and local measurements of H₀. This part provides the first-layer cosmological parameterization and observational confrontation, establishing UFG as a mathematically consistent and observationally viable alternative to the current cosmological paradigm.