Add touch-to-logical coordinate mapping for UI

Implements tapToLogical() to convert normalized touch coordinates to orientation-aware logical screen coordinates. Adds TouchRegistry hit testing for interactive UI elements and header back button. Touch gestures now work correctly across all screen orientations (Portrait, Landscape, etc.) by inverting the rotateCoordinates transform.

lib/GfxRenderer/GfxRenderer.h

@@ -135,6 +135,11 @@ class GfxRenderer {
   void clearScreen(uint8_t color = 0xFF) const;
   void getOrientedViewableTRBL(int* outTop, int* outRight, int* outBottom, int* outLeft) const;
 
+  // Map a touch tap (normalized 0..1 in panel-native orientation, from
+  // InputManager::wasTouchTap) to logical screen coordinates matching the Rects the
+  // UI draws in. Inverse of rotateCoordinates() for the current orientation.
+  void tapToLogical(float nx, float ny, int& outX, int& outY) const;
+
   // Tiled grayscale strip target. While active, drawPixel() and clearScreen()
   // operate on `scratch` (panelWidthBytes * stripRows bytes, holding physical
   // rows [stripY0, stripY0 + stripRows)) instead of the framebuffer; pixels