Supplement to PFUS V14.0: Rigorous Derivation of the Cosmic Intrinsic Scale Constant π₁=12 to 11

Within the axiomatic framework of the PFUS V14.0 Bi‑Frustum Unified Cosmological System and Four‑Dimensional Mathematics V6.0, this paper presents a complete, rigorous, parameter‑free, non‑fitted, and ad‑hoc‑free formal derivation of the cosmic intrinsic scale constant π₁=12 to 11. We prove that π₁ is not an empirical parameter, but an ontologically necessary consequence jointly constrained by the maximum stable dimension D_max=11, the geometric uniqueness of the 45° coaxial double‑cone frustum, topological compact closure, Banach completeness, and the Five‑Element rigid closed cycle. We fully reconstruct the generative mechanism of π₁ from five consistent pathways: dimensional stability, hierarchical nesting, ring‑on‑ring structure, topological closure, and geometric conservation. We rigorously establish the absolute uniqueness and non‑arbitrariness of the value. This paper can be published independently as a core theorem article on fundamental cosmic constants within the PFUS system, used for teaching, and archived permanently.