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

2 files changed, 32 insertions, 5 deletions

diff --git a/src/gpu/effects/cnn_v2_effect.cc b/src/gpu/effects/cnn_v2_effect.cc
index 366a232..d412154 100644
--- a/src/gpu/effects/cnn_v2_effect.cc
+++ b/src/gpu/effects/cnn_v2_effect.cc
@@ -19,6 +19,7 @@ CNNv2Effect::CNNv2Effect(const GpuContext& ctx)
       static_params_buffer_(nullptr),
       static_features_tex_(nullptr),
       static_features_view_(nullptr),
+      linear_sampler_(nullptr),
       layer_pipeline_(nullptr),
       weights_buffer_(nullptr),
       input_mip_tex_(nullptr),
@@ -36,6 +37,7 @@ CNNv2Effect::CNNv2Effect(const GpuContext& ctx, const CNNv2EffectParams& params)
       static_params_buffer_(nullptr),
       static_features_tex_(nullptr),
       static_features_view_(nullptr),
+      linear_sampler_(nullptr),
       layer_pipeline_(nullptr),
       weights_buffer_(nullptr),
       input_mip_tex_(nullptr),
@@ -221,6 +223,20 @@ void CNNv2Effect::create_textures() {
 }
 
 void CNNv2Effect::create_pipelines() {
+  // Create linear sampler for bilinear interpolation
+  WGPUSamplerDescriptor sampler_desc = {};
+  sampler_desc.addressModeU = WGPUAddressMode_ClampToEdge;
+  sampler_desc.addressModeV = WGPUAddressMode_ClampToEdge;
+  sampler_desc.addressModeW = WGPUAddressMode_ClampToEdge;
+  sampler_desc.magFilter = WGPUFilterMode_Linear;
+  sampler_desc.minFilter = WGPUFilterMode_Linear;
+  sampler_desc.mipmapFilter = WGPUMipmapFilterMode_Linear;
+  sampler_desc.lodMinClamp = 0.0f;
+  sampler_desc.lodMaxClamp = 32.0f;
+  sampler_desc.maxAnisotropy = 1;
+
+  linear_sampler_ = wgpuDeviceCreateSampler(ctx_.device, &sampler_desc);
+
   // Static features compute pipeline
   size_t shader_size = 0;
   const char* static_code = (const char*)GetAsset(AssetId::ASSET_SHADER_CNN_V2_STATIC, &shader_size);
@@ -238,8 +254,8 @@ void CNNv2Effect::create_pipelines() {
   shader_desc.nextInChain = &wgsl_src.chain;
 
   // Create bind group layout for static features compute
-  // Bindings: 0=input_tex, 1=input_mip1, 2=input_mip2, 3=depth_tex, 4=output, 5=params
-  WGPUBindGroupLayoutEntry bgl_entries[6] = {};
+  // Bindings: 0=input_tex, 1=input_mip1, 2=input_mip2, 3=depth_tex, 4=output, 5=params, 6=linear_sampler
+  WGPUBindGroupLayoutEntry bgl_entries[7] = {};
 
   // Binding 0: Input texture (mip 0)
   bgl_entries[0].binding = 0;
@@ -278,8 +294,13 @@ void CNNv2Effect::create_pipelines() {
   bgl_entries[5].buffer.type = WGPUBufferBindingType_Uniform;
   bgl_entries[5].buffer.minBindingSize = sizeof(StaticFeatureParams);
 
+  // Binding 6: Linear sampler (for bilinear interpolation)
+  bgl_entries[6].binding = 6;
+  bgl_entries[6].visibility = WGPUShaderStage_Compute;
+  bgl_entries[6].sampler.type = WGPUSamplerBindingType_Filtering;
+
   WGPUBindGroupLayoutDescriptor bgl_desc = {};
-  bgl_desc.entryCount = 6;
+  bgl_desc.entryCount = 7;
   bgl_desc.entries = bgl_entries;
 
   WGPUBindGroupLayout static_bgl = wgpuDeviceCreateBindGroupLayout(ctx_.device, &bgl_desc);
@@ -398,7 +419,7 @@ void CNNv2Effect::update_bind_group(WGPUTextureView input_view) {
   }
 
   // Create bind group for static features compute
-  WGPUBindGroupEntry bg_entries[6] = {};
+  WGPUBindGroupEntry bg_entries[7] = {};
 
   // Binding 0: Input (mip 0)
   bg_entries[0].binding = 0;
@@ -425,9 +446,13 @@ void CNNv2Effect::update_bind_group(WGPUTextureView input_view) {
   bg_entries[5].buffer = static_params_buffer_;
   bg_entries[5].size = sizeof(StaticFeatureParams);
 
+  // Binding 6: Linear sampler
+  bg_entries[6].binding = 6;
+  bg_entries[6].sampler = linear_sampler_;
+
   WGPUBindGroupDescriptor bg_desc = {};
   bg_desc.layout = wgpuComputePipelineGetBindGroupLayout(static_pipeline_, 0);
-  bg_desc.entryCount = 6;
+  bg_desc.entryCount = 7;
   bg_desc.entries = bg_entries;
 
   static_bind_group_ = wgpuDeviceCreateBindGroup(ctx_.device, &bg_desc);
@@ -563,6 +588,7 @@ void CNNv2Effect::cleanup() {
   if (static_bind_group_) wgpuBindGroupRelease(static_bind_group_);
   if (static_params_buffer_) wgpuBufferRelease(static_params_buffer_);
   if (static_pipeline_) wgpuComputePipelineRelease(static_pipeline_);
+  if (linear_sampler_) wgpuSamplerRelease(linear_sampler_);
 
   if (layer_pipeline_) wgpuComputePipelineRelease(layer_pipeline_);
   if (weights_buffer_) wgpuBufferRelease(weights_buffer_);
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