Based on two first principles without additional premises, this paper constructs a fully geometric unified theory of fundamental physics, achieving self-consistent compatibility between general relativity and quantum mechanics, and completing the ultimate unification of the four fundamental interactions, the origin of matter, dark universe physics, and quantum rules. The theory is founded on two core axioms: Axiom 1: Scale Self-Duality Invariance, which states that physical laws remain form-invariant under scale-reciprocal transformations with the Planck length as the mirror; Axiom 2: Ontology of Cosmic Spacetime, which defines the cosmic spatial topology as a closed 3-sphere \(S^3\) embedded in four-dimensional Euclidean space, with the complete spacetime being the direct product Lorentzian manifold \(M=S^3 \times \mathbb{R}\). From the above two axioms, this paper rigorously derives the Einstein field equations of general relativity and the complete gauge group structure of the Standard Model of particle physics, without introducing extra dimensions, free parameters, unknown particles, or artificial assumptions. It elucidates the geometric origins of fermion spin, the Pauli exclusion principle, charge quantization, and inertial mass, provides a self-consistent explanation for the nature of dark matter and dark energy as well as the dynamical mechanism of cosmic accelerated expansion, and fully reconstructs the spacetime geometric roots of quantum phenomena, fundamentally eliminating the divide between the macroscopic and microscopic, and between the classical and quantum realms. This paper supplements the missing key quantitative derivation details in the original framework, achieves precise alignment with the latest 2026 cosmological and particle physics observational data, and presents a set of falsifiable quantitative predictions with clear experimental test schemes. The theory offers a logically consistent, minimalist, and complete geometric unification solution for fundamental physics. Copyright © 2026 Zheng Xinyu (All Rights Reserved). This work is the original research achievement of the author, without plagiarism or copyright disputes. Without the author's written permission, no individual or organization may reproduce, distribute, adapt, or use this work for any purpose.