gpu_portfolio.rs: deleted CPU simulate_batch() path (GPU path exists),
get_portfolio_state() returns &CudaSlice (was: download to [f32;8])
branching.rs: GPU-native argmax per branch, GPU gather+mean for Q
aggregation, GPU affine+floor for action decomposition, GPU sub→abs→
max for weight comparison in tests
gpu_tensor.rs: added pub cuda_data() accessor
stream_ops.rs: fixed CudaView type mismatch in dtod_copy
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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