Add regression coverage for run_vulkan launcher path selection

[cursor]

Summary

• Add a deterministic script-level regression test for scripts/run_vulkan.sh.
• Register the new test in CTest as regression_run_vulkan_launcher.

Risky behavior now covered

• Launcher path resolution when invoked from scripts/ now correctly prefers sibling ../release binaries.
• Architecture-specific binary selection (idtech3.aarch64 on aarch64) and fallback to idtech3 when arch-specific binary is missing.
• Argument forwarding to the selected engine executable remains intact.

Test files added/updated

• Added: tests/scripts/test_run_vulkan.sh
• Updated: CMakeLists.txt (adds CTest registration)

Why this materially reduces regression risk

• run_vulkan.sh recently changed engine discovery behavior; regressions here can silently launch the wrong binary or fail on ARM systems.
• The new tests exercise real execution paths with isolated stubs and controlled uname -m responses, avoiding GPU/game-data dependencies while validating high-impact launcher behavior.
• Coverage targets a shared launcher used in core start-up workflows, giving high signal for low maintenance cost.

Validation

• bash tests/scripts/test_run_vulkan.sh /workspace/scripts/run_vulkan.sh
• ctest --test-dir /workspace/build-vk-Release -R regression_run_vulkan_launcher --output-on-failure