fix: Resolve CNN effect black screen bug (framebuffer capture + uniforms)

Two bugs causing black screen when CNN post-processing activated:

1. Framebuffer capture timing: Capture ran inside post-effect loop after
   ping-pong swaps, causing layers 1+ to capture wrong buffer. Moved
   capture before loop to copy framebuffer_a once before post-chain starts.

2. Missing uniforms update: CNNEffect never updated uniforms_ buffer,
   leaving uniforms.resolution uninitialized (0,0). UV calculation
   p.xy/uniforms.resolution produced NaN, causing all texture samples
   to return black. Added uniforms update in update_bind_group().

Files modified:
- src/gpu/effect.cc: Capture before post-chain (lines 308-346)
- src/gpu/effects/cnn_effect.cc: Add uniforms update (lines 132-142)
- workspaces/main/shaders/cnn/cnn_layer.wgsl: Remove obsolete comment
- doc/CNN_DEBUG.md: Historical debugging doc
- CLAUDE.md: Reference CNN_DEBUG.md in historical section

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

1 files changed, 1 insertions, 0 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index 3d41cb7..a52dfce 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -52,6 +52,7 @@
 #   doc/PLATFORM_ANALYSIS.md
 #   doc/PLATFORM_SIDE_QUEST_SUMMARY.md
 #   doc/PEAK_FIX_SUMMARY.md
+#   doc/CNN_DEBUG.md - CNN post-processing binding bug resolution
 #
 # Agent Handoffs:
 #   doc/HANDOFF_CLAUDE.md