Silk DE System Contract: Deterministic Rendering and Startup Validation

Architectural enforcement of the Silk DE System Contract. It details how shared layout constants and semantics are explicitly versioned within crates/silkbar-model, acting as the single source of truth for both the silkbar state producer and the sexdisplay renderer, The overview explores the implementation of startup contract validation, fail-open rendering policies designed to prevent black screens, and the strict VBLANK-synchronized execution pipeline that guarantees visual liveness across the operating system.