refactor(effects): drop the unused composite acrylic shader

The acrylic material carried a full composite shader — vertex and
fragment source, compile and link helpers, the program handle and seven
uniform locations — that nothing ever invoked. The acrylic is composited
on the ImGui draw list, not through this program.

- Remove the dead shader source, its compile/link helpers, the program
  and uniform fields, and the compile/link/cleanup steps in init and
  shutdown. No behaviour change; init no longer builds a program that is
  never bound.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/effects/acrylic.h

@@ -352,12 +352,6 @@ private:
      */
     void applyBlur(float radius, bool ignoreMultiplier = false);
     
-    /**
-     * @brief Composite final acrylic appearance
-     */
-    void compositeAcrylic(const ImVec2& pMin, const ImVec2& pMax,
-                          const AcrylicParams& params);
-    
     /**
      * @brief Check if effect should be skipped (settings/quality)
      */
@@ -406,16 +400,6 @@ private:
     // Noise texture
     NoiseTexture noiseTexture_;
     
-    // Composite shader (tint + noise overlay)
-    GLuint compositeShader_ = 0;
-    GLint uCompositeTintColor_ = -1;
-    GLint uCompositeTintOpacity_ = -1;
-    GLint uCompositeLuminosity_ = -1;
-    GLint uCompositeNoiseOpacity_ = -1;
-    GLint uCompositeBlurTex_ = -1;
-    GLint uCompositeNoiseTex_ = -1;
-    GLint uCompositeTexScale_ = -1;
-
 #ifdef DRAGONX_USE_DX11
     // ---- DX11 acrylic resources (used instead of GL objects above) ----
     ID3D11Device*              dx_device_       = nullptr;