add separate render path when sleep.bmp is found in root of sd card

src/screens/SleepScreen.cpp

@@ -2,10 +2,23 @@
 
 #include <GfxRenderer.h>
 
+#include "SD.h"
 #include "config.h"
 #include "images/CrossLarge.h"
 
 void SleepScreen::onEnter() {
+  // Look for sleep.bmp on the root of the sd card to determine if we should
+  // render a custom sleep screen instead of the default.
+  auto file = SD.open("/sleep.bmp");
+  if (file) {
+    renderCustomSleepScreen(file);
+    return;
+  }
+
+  renderDefaultSleepScreen();
+}
+
+void SleepScreen::renderDefaultSleepScreen() {
   const auto pageWidth = GfxRenderer::getScreenWidth();
   const auto pageHeight = GfxRenderer::getScreenHeight();
 
@@ -16,3 +29,16 @@ void SleepScreen::onEnter() {
   renderer.invertScreen();
   renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
 }
+
+void SleepScreen::renderCustomSleepScreen(File file) {
+  Serial.println("Rendering custom sleep screen from sleep.bmp");
+
+  const auto pageWidth = GfxRenderer::getScreenWidth();
+  const auto pageHeight = GfxRenderer::getScreenHeight();
+
+  renderer.clearScreen();
+
+  renderer.drawCenteredText(UI_FONT_ID, pageHeight / 2 + 70, "CUSTOM SLEEP SCREEN", true, BOLD);
+
+  renderer.displayBuffer(EInkDisplay::HALF_REFRESH);
+}

src/screens/SleepScreen.h

@@ -1,8 +1,11 @@
 #pragma once
+#include "SD.h"
 #include "Screen.h"
 
 class SleepScreen final : public Screen {
  public:
   explicit SleepScreen(GfxRenderer& renderer, InputManager& inputManager) : Screen(renderer, inputManager) {}
   void onEnter() override;
+  void renderDefaultSleepScreen();
+  void renderCustomSleepScreen(File file);
 };