tests: add Vulkan vegetation dispatch ordering regression coverage

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Summary

• add tests/scripts/test_vk_vegetation_dispatch_order.sh to guard the Vulkan vegetation-wind bugfix path
• wire the new script into CTest as test_vk_vegetation_dispatch_order in CMakeLists.txt

Risky behavior now covered

• prevents regressions where vk_vegetation_wind_dispatch() is called too early from vk_begin_frame (before vegetation staging is filled)
• enforces that dispatch + staging clear happen from RB_EndSurface under the SURF_VEGETATION + PostFX_VegWind_IsEnabled() gated path

Test files added/updated

• added: tests/scripts/test_vk_vegetation_dispatch_order.sh
• updated: CMakeLists.txt (CTest registration)

Why this materially reduces regression risk

This coverage protects a real bugfix in a high-blast-radius render flow: vegetation animation compute work previously ran before tessellation data upload and silently no-op’d (vertexCount==0). The test asserts both sides of the contract (presence in RB_EndSurface, absence in vk_begin_frame) so future refactors cannot accidentally reintroduce frame-ordering regressions without failing CI.

Validation

• tests/scripts/test_vk_vegetation_dispatch_order.sh
• ctest -R test_vk_vegetation_dispatch_order --output-on-failure (after reconfigure)