ECI v5.0.2 — Entanglement, Complexity, Information: a phenomenological framework with DESI DR2 + Pantheon+ MCMC

v5.0.2 phenomenological companion (EPJ C / astro-ph.CO track) of the ECI framework. A non-minimally coupled thawing quintessence χ with coupling ξ_χ R χ²/2 is confronted to DESI DR2 BAO + Pantheon+ SN via a 4-chain MPI MCMC (19,700 samples, Gelman–Rubin R−1 = 0.036). Main result: ξ_χ = 0.003 +0.065/−0.070 at 68% CL (χ₀ = M_P/10); Savage–Dickey Bayes factor BF₀₁ ≈ 1. The posterior is weakly informed by DR2+SN precision (posterior/prior half-width ratio ≈ 0.7), interpreted as a consistency check rather than a detection. Includes DR3/LSST Fisher structural-null, χ(z) caveat, Wolf (2025) scalar-field ΛCDM consistency, and Pan & Ye (2026) NMC screening constraints. The paper is a framework synthesis, not a derivation — it assembles six research programs (2022–2026) into a single predictive canvas and lists seven falsifiable predictions (DESI DR3, Euclid DR1, CMB-S4, SO, Eöt-Wash, optical clocks, KM3NeT).