CNN v2: bilinear mip-level sampling and UI improvements

**CNN v2 Changes:**
- Replace point sampling with bilinear interpolation for mip-level features
- Add linear sampler (binding 6) to static features shader
- Update CNNv2Effect, cnn_test, and HTML tool

**HTML Tool UI:**
- Move controls to floating bottom bar in central view
- Consolidate video controls + Blend/Depth/Save PNG in single container
- Increase left panel width: 300px → 315px (+5%)
- Remove per-frame debug messages (visualization, rendering logs)

**Technical:**
- WGSL: textureSample() with linear_sampler vs textureLoad()
- C++: Create WGPUSampler with Linear filtering
- HTML: Change sampler from 'nearest' to 'linear'

handoff(Claude): CNN v2 now uses bilinear mip-level sampling across all tools

1 files changed, 1 insertions, 0 deletions

diff --git a/src/gpu/effects/cnn_v2_effect.h b/src/gpu/effects/cnn_v2_effect.h
index 8a2e1b6..d530d3b 100644
--- a/src/gpu/effects/cnn_v2_effect.h
+++ b/src/gpu/effects/cnn_v2_effect.h
@@ -64,6 +64,7 @@ private:
   WGPUBuffer static_params_buffer_;
   WGPUTexture static_features_tex_;
   WGPUTextureView static_features_view_;
+  WGPUSampler linear_sampler_;
 
   // CNN layers (storage buffer architecture)
   WGPUComputePipeline layer_pipeline_;      // Single pipeline for all layers