feat: Add displayGrayscaleBase method for differential refresh

(#2334)

Introduces a new display method that prepares the framebuffer as a base
frame for grayscale overlays. On X3 panels, this uses the OEM
differential base waveform (AA-pre-BW) without forcing a resync. Other
panels fall back to normal display with configurable refresh mode.


Dependent upon matching SDK commit to work

lib/GfxRenderer/GfxRenderer.h

@@ -218,6 +218,16 @@ class GfxRenderer {
   // Grayscale functions
   void setRenderMode(const RenderMode mode) { this->renderMode = mode; }
   RenderMode getRenderMode() const { return renderMode; }
+  // Grayscale preconditioning settle pass (no-op on X4). The rect overload
+  // takes the gray region in LOGICAL screen coordinates and rotates it to the
+  // panel; the no-arg overload settles the full frame. Call after the BW base
+  // frame is displayed and before the grayscale planes are written.
+  void preconditionGrayscale() const;
+  void preconditionGrayscale(int x, int y, int w, int h) const;
+  // Display the framebuffer as the base frame for a grayscale overlay that
+  // follows (X3: OEM differential base waveform; others: plain display with
+  // `fallback`).
+  void displayGrayscaleBase(HalDisplay::RefreshMode fallback = HalDisplay::HALF_REFRESH) const;
   void copyGrayscaleLsbBuffers() const;
   void copyGrayscaleMsbBuffers() const;
   void displayGrayBuffer() const;