Document PRK.Client options inventory and panel mockups

Produce a canonical Typst design brief and compiled PDF under Docs for the PRK.Client options-panel investigation. Assume PR #2621 is merged: one persisted live ViewDistance replaces the five distances. Preserve source-backed existing/partial/new distinctions; cover player options, technical-only configuration, persistence/application architecture, priorities and acceptance criteria. Include annotated conceptual mockups, explicitly distinguish proposed UI from implemented functionality. Scope is documentation only, not client implementation. Acceptance verified: Docs/PRK-Client-Options-Design.typ and .pdf contain a 15-page source-backed brief with six annotated vector mockups (Display, Graphics, Audio, Controls, Chat, Combat/Accessibility), configuration inventory, persistence/application contracts, delivery gates and source map. PR #2621 is explicitly an assumed baseline. Typst 0.15.1 compilation passed; all 15 rendered pages visually inspected and final changed page rechecked. PDF extraction verified 15 pages, six mockups, expected sections and no replacement glyphs. git diff --check passed. Documentation only on docs/client-options-design; no client implementation, commit or PR.