Strided batched matmul with bias, GELU/ReLU and residual in the epilogue, layer
norm, softmax, window partition, pooling, patch embedding, RoPE and neck kernels
(WGSL, all tested against CPU definitions). GpuEncoder keeps activations on the
GPU and returns the 64x64 level and the decoder's skip features. On the RX 7900
GRE one frame encodes in 0.29 s (debug build) against 2.1 s on the CPU in release;
errors 6.8e-6 vs PyTorch, 1.2e-5 vs the CPU path.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>