ReplaceAlphaWithStencil's blue-to-alpha check sat after a branch that already
catches every replaceBlend except NO and READ_FRAMEBUFFER - so it was dead, and
blue-to-alpha draws could come back REPLACE_ALPHA_YES or DUALSOURCE and pick up
stencil-to-alpha on top of the blue-to-alpha setup. Moved it above.
The D3D11 fragment shader applied nointerpolation to v_color0 but not v_color1,
and in HLSL it's the PS input declaration that decides - so flat shading was lost
for the specular term. The vertex shader already marks both.