refactor: Bundle GPU context into GpuContext struct

- Created GpuContext struct {device, queue, format}
- Updated Effect/PostProcessEffect to take const GpuContext&
- Updated all 19 effect implementations
- Updated MainSequence.init() and LoadTimeline() signatures
- Updated generated timeline files
- Updated all test files
- Added gpu_get_context() accessor and fixture.ctx() helper

Fixes test_mesh.cc compilation error from g_device/g_queue/g_format conflicts.
All targets build successfully.

1 files changed, 9 insertions, 4 deletions

diff --git a/src/gpu/gpu.h b/src/gpu/gpu.h
index b8f58b2..c4d1993 100644
--- a/src/gpu/gpu.h
+++ b/src/gpu/gpu.h
@@ -9,6 +9,13 @@
 struct PlatformState; // Forward declaration
 class Effect; // Forward declaration
 
+// GPU context bundling device, queue, and surface format
+struct GpuContext {
+  WGPUDevice device;
+  WGPUQueue queue;
+  WGPUTextureFormat format;
+};
+
 // Basic wrapper for WebGPU buffers
 struct GpuBuffer {
   WGPUBuffer buffer;
@@ -39,10 +46,8 @@ void gpu_resize(int width, int height);
 void gpu_simulate_until(float time);
 void gpu_add_custom_effect(Effect* effect, float start_time, float end_time, int priority);
 
-// Expose WebGPU globals for custom effects (debug builds only)
-extern WGPUDevice g_device;
-extern WGPUQueue g_queue;
-extern WGPUTextureFormat g_format;
+// Get GPU context for custom effects (debug builds only)
+const GpuContext* gpu_get_context();
 #endif
 void gpu_shutdown();