Add live world-shadow quality levels to PRK.Client options

Replace the wired World Shadows on/off control with an Off/Low/Medium/High dropdown that changes the cascaded world shadow-map resolution live. Keep Character Shadows separate. Preserve the committed live resource/variant replacement path and render buffering restart behavior. Define one typed quality-to-resolution mapping, include quality in persisted machine settings/startup features/presets, retain compatibility with the existing WorldShadows boolean preference, support an explicit quality environment override while honoring the legacy disable override, and do not conflate capability fallback with saved request. Implemented; user authorized completion/commit: World Shadows is Off / Low (1024 px) / Medium (2048 px) / High (4096 px). One typed mapping drives allocation, framebuffer dimensions, viewport/scissor and cascade fitting. The live shadow swap receives quality and recreates resources when map size changes; shader variants change only across Off/non-Off. Character-shadow quality remains separate and render buffering remains restart-only. Machine persistence adds WorldShadowQuality while retaining the previous WorldShadows bool: old false loads Off and old true with no quality loads High. New PRK_WORLD_SHADOWS quality override locks the dropdown; legacy PRK_DISABLE_SHADOWS=true wins and forces Off. Capability fallback remains effective renderer state, separate from the saved request. Low/Medium/High presets now choose corresponding world quality. Validation: 363 available regressions passed, plus the final world-shadow dropdown label/selection test; non-automation Release client build passed with zero warnings/errors, Skia/AO asset Graphics render reviewed and git diff --check passed. The same five stock-profile/install-tree fixtures remain excluded. User requested no native reload test and accepted the implementation for commit. Committed as 480d915fb (feature: Add live world shadow quality levels) on feature/client-options-window. Working tree clean; no push or deployment.