fix: Capture scene framebuffer before post-processing for CNN effect

CNNEffect's "original" input was black because FadeEffect (priority 1) ran
before CNNEffect (priority 1), fading the scene. Changed framebuffer capture
to use framebuffer_a (scene output) instead of current_input (post-chain).

Also add seq_compiler validation to detect post-process priority collisions
within and across concurrent sequences, preventing similar render order issues.

Updated stub_types.h WGPULoadOp enum values to match webgpu.h spec.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions