fix(headless): add nullptr checks for GPU resource creation

- NodeRegistry::create_texture: skip texture creation when device is nullptr
- Post-process helpers: skip pipeline/bind group creation in headless mode
- SamplerCache: return nullptr for headless mode
- BindGroupLayoutBuilder/BindGroupBuilder: skip creation with null device
- RenderPipelineBuilder: skip shader module and pipeline creation in headless
- PlaceholderEffect: skip sampler creation in headless mode
- RotatingCubeEffect: early return in constructor for headless mode

WIP: Some effects (GaussianBlur, etc.) still need headless checks

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

1 files changed, 5 insertions, 0 deletions

diff --git a/src/gpu/sampler_cache.h b/src/gpu/sampler_cache.h
index 7149921..b3fdb19 100644
--- a/src/gpu/sampler_cache.h
+++ b/src/gpu/sampler_cache.h
@@ -39,6 +39,11 @@ class SamplerCache {
   }
 
   WGPUSampler get_or_create(WGPUDevice device, const SamplerSpec& spec) {
+    // Headless mode: skip sampler creation
+    if (device == nullptr) {
+      return nullptr;
+    }
+
     auto it = cache_.find(spec);
     if (it != cache_.end())
       return it->second;