Migrates the remaining 4 forward sites:
- VSN Linear_1 (x6 groups): adds 6 per-group RELU_BIAS shapes to the
relu_bias cache; migrates sgemm_f32_ldb + launch_add_bias_relu_f32_raw
pairs to sgemm_f32_fused_relu_bias.
- VSN Linear_2 (x6 groups, single shape (1, B, VSN_HIDDEN, VSN_HIDDEN)):
migrates to sgemm_f32_fused_bias.
- GLU value head + gate (launch_vsn_glu_branch Steps 3-4): migrates to
sgemm_f32_fused_bias with per-stream workspace selection.
Also fixes a partial-refactor leak in forward_online_raw — the
sequential branch fallback (distinct_branches=false) was still on the
unfused sgemm_f32 + launch_add_bias_relu_f32_raw pair while its
multi-stream sibling already used the fused epilogue. Now both code
paths take the fused-first contract.
Layout fingerprint unchanged (no params buffer changes).
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