feat(rendering): gate sky bakes by device capabilities

[JeanPhilippeKernel]

Summary

• gate atmosphere and HDRI environment bakes on explicit Vulkan image-format capabilities, retaining the fallback snapshot with a readable reason when unavailable
• coalesce small animated primary-sun updates while preserving immediate bakes for availability changes and rotations of at least 5 degrees
• consolidate shared Vulkan image-capability probes and keep new reason APIs on cstring

Validation

• cmake --build --preset Darwin_arm64_Debug --target ZEngineTests --parallel 8
• ./Result.Darwin.arm64.Debug/ZEngine/tests/Debug/ZEngineTests --gtest_filter=SkyEnvironmentTest.*:SkyAtmosphereViewPassTest.*:RenderGraphDeclarationTest.*:RenderGraphSynchronizationTest.* --gtest_brief=1 (38 passed)
• launched SampleProject in the Debug editor from the runtime output directory

Part of #808.