Decode RGB9E5 inputs in failed upscale fallbacks - #425

What this fixes

When an upscale network fails to translate on AMD, entering Kokiri or changing dynamic resolution can turn the scene into bright neon colors.

Why merge

• Samples the declared RGB9E5 view using the existing upscale shader and its scene-color conversion.
• Checks sampling, linear filtering and storage-format support before creating typed views.
• Keeps gameplay TAAU history separate. Movie paths, existing environment controls and unsupported-format fallbacks remain unchanged.

Change

gpu/vk/vk_draw.cpp: share the existing typed helper and use it for compatible RGB9E5 fallback inputs.
tests/test_upscale_fallback.py: exercise the actual fallback function across 13 routing and capability cases without Vulkan.

Tested

• python -I -B tests/test_upscale_fallback.py --cxx clang++ checks the routing and unsupported-feature fallbacks. Fails on the old code, passes now.
• Real captured input: the original blit matches native output byte for byte; the typed shader passes 8,364 channel checks against spatial decoding and interpolation.
• RX 9070 XT, Windows: 116 seconds, 2,040 presents, zero VUIDs. The sampled neon transition is gone; steady Kokiri still renders. No game data is included.

Not covered

• Tested on AMD only.
• This is a spatial fallback. Neural temporal reconstruction and view overrides, additional mips or layers are outside this change.