Unified Chordal Resonance Theory (UCRT): Gravity, Particles, and Cosmology from a Multitonal Vibrational Substrate Full manuscript (12 pages). First version. Original theoretical physics preprint proposing that gravity, the Standard Model, dark matter, dark energy, and cosmology emerge from a single multitonal vibrational scalar field Psi_total with dominant nonlinear coupling lambda_nl. The baseline hum Psi_total,0 at near-Planck frequencies produces beat interference and resonance cascades, yielding emergent phenomena including fermion mass hierarchies, gauge symmetries on S^3, fuzzy black hole cores, hybrid DM halos with subhalo suppression below ~10^8 solar masses, and late-time dark energy from phase diffusion. Resolves black hole singularities via diffusion, missing satellites problem via destructive interference, and matter-antimatter asymmetry via phase driven CP violation. Consistent with Planck CMB, DESI BAO, JWST ultra-faint dwarfs, and precision flavor data. Falsifiable via GW echoes/sidebands (LISA), B-mode bumps (CMB-S4), DM cores/subhalo counts (JWST/LSST), ~10 TeV resonances (FCC), and phonon analogs in tabletop experiments. AI-assisted draft (Grok by xAI) for structuring, mathematical expressions, LaTeX formatting, and continuity review. Author (Jessica Bower) has reviewed, edited, and takes full responsibility for all content. Keywords: unified theory, emergent gravity, quantum gravity, multitonal scalar field, fuzzy dark matter, asymptotic safety, parametric resonance, beat frequencies, missing satellites problem, entropic gravity, dark energy decoherence, gauge emergence, Yukawa hierarchies