DX11 alpha blending is never enabled: `SetBlendState` is dead code

[CanReader]

src/Graphics/DirectX11/DirectX11Renderer.cpp:875, :877

grep -rn "SetBlendState" across engine + game returns only the function definition (:875) and its
declaration: no call sites. OMSetBlendState appears exactly once in the whole DX11 backend, at :877,
inside that never-called function.

So DX11 runs with the default blend state (blending disabled) permanently. Concrete symptom: SleakCraft's
water renders fully opaque on -r d3d11 despite SetOpacity(0.7f).

Severity: visual.

Found by a full audit of the graphics layer. Assessed severity: visual.