[r0naldoom]

Summary

Adds an opt-in classic centered bottom HUD layout while preserving the responsive HUD as the default.

Refs #604

Root cause

fe407e1b anchors the three bottom HUD bands to the window edges and center (BottomHud{Left,Center,Right}Transform). At 16:9 the world shows between them and each band ends on an internal cut of the artwork (x=152 in newui_menu01, x=488 in newui_menu03). Details and screenshots in #604.

Fix

• Adds [UI] BottomHudClassic (0 by default; 1 enables Classic).
• Adds the live Classic bottom HUD option to the Options window.
• Applies a single centered 640 logical-pixel HUD transform to the left, center, right, and experience-rail regions when enabled.
• Persists the preference and applies it during startup.

Test plan

• clang-format 21.1.8 checks on changed ranges.
• cppcheck on the changed C++ sources with the CI suppressions.
• Release CMake build.
• ctest --output-on-failure — 207/207 tests passed, including the classic-HUD scaling coverage.
• Wayland/Vulkan runtime: toggled the option live at 1920×1080; config.ini persisted BottomHudClassic=1; log selected the Vulkan SDL_gpu driver.
• OFF screenshot: https://github.com/user-attachments/assets/c437386e-a897-4264-9fe1-785ed2c7959d
• ON screenshot: https://github.com/user-attachments/assets/026ae4fb-ef36-4cbc-8fc5-e6c190d2db72
• Windows not tested.
• macOS not tested.

Checklist

• I have read and followed docs/CODING_RULES.md.
• I have built the project locally (see docs/build/README.md).
• Changes are focused on one concern; the diff is as small as it reasonably can be.

[alandarev]

by the way, this will be fixed in #610