- fmha_multihead_capi.cu: SMEM formula matches standalone test
Added cudaFuncSetAttribute for dynamic SMEM > 48KB
- fmha_multihead_op.py: pad K/V to N=128 when N<128
(kernel softmax loop is hardcoded to SK_TILE=128)
- Removed fmha_multihead_launch.cu (ATen approach, didn't work)
- Removed test_p3_ctypes_minimal.py (superseded by main test)