Book IV closure: coupling ledger and microcosm completion

Book IV closes by assembling the T^2-fiber microcosm as a readout stack: fine-structure and mass-ratio quantities are empirical readouts of the iota_tau coupling structure; chemistry and molecular geometry are downstream CR-address / defect-regime organizations; condensed phases, superfluids, superconductors, magnetism, and fluids are ensemble regimes of the same universal defect tuple. The stated inter-sector coupling ledger has no fitted dimensionless free parameters; the neutron mass remains the dimensional calibration anchor. The microcosm is therefore complete as an ontology-and-status ledger: the carrier roles are assigned, while detailed derivation chains for precision quantities and composite regimes remain in the physics-readout supplement.