feat: add SDCardManager rename method and EInkDisplay improvements

- Add rename() method to SDCardManager for file/directory moves
- Improve EInkDisplay grayscale handling

libs/display/EInkDisplay/src/EInkDisplay.cpp

@@ -399,11 +399,21 @@ void EInkDisplay::copyGrayscaleBuffers(const uint8_t* lsbBuffer, const uint8_t*
 #ifdef EINK_DISPLAY_SINGLE_BUFFER_MODE
 /**
  * In single buffer mode, this should be called with the previously written BW buffer
- * to reconstruct the RED buffer for proper differential fast refreshes following a
+ * to restore proper BW state after a grayscale display.
- * grayscale display.
+ * 
+ * The approach: Don't call grayscaleRevert() at all. Instead, just sync the RAMs with
+ * BW data and clear the grayscale mode flag. The physical pixels will stay in their
+ * current grayscale states, but subsequent refreshes will naturally transition them
+ * as the new BW content is displayed.
  */
 void EInkDisplay::cleanupGrayscaleBuffers(const uint8_t* bwBuffer) {
+  // Clear grayscale mode - we don't want grayscaleRevert to be called later
+  // because the RAMs won't have valid grayscale data anymore
+  inGrayscaleMode = false;
+  
+  // Sync both RAMs with BW content for proper fast refresh behavior
   setRamArea(0, 0, DISPLAY_WIDTH, DISPLAY_HEIGHT);
+  writeRamBuffer(CMD_WRITE_RAM_BW, bwBuffer, BUFFER_SIZE);
   writeRamBuffer(CMD_WRITE_RAM_RED, bwBuffer, BUFFER_SIZE);
 }
 #endif
@@ -416,8 +426,7 @@ void EInkDisplay::displayBuffer(RefreshMode mode) {
 
   // If currently in grayscale mode, revert first to black/white
   if (inGrayscaleMode) {
-    inGrayscaleMode = false;
+    grayscaleRevert();  // grayscaleRevert() sets inGrayscaleMode = false internally
-    grayscaleRevert();
   }
 
   // Set up full screen RAM area
@@ -477,8 +486,7 @@ void EInkDisplay::displayWindow(uint16_t x, uint16_t y, uint16_t w, uint16_t h)
 
   // displayWindow is not supported while the rest of the screen has grayscale content, revert it
   if (inGrayscaleMode) {
-    inGrayscaleMode = false;
+    grayscaleRevert();  // grayscaleRevert() sets inGrayscaleMode = false internally
-    grayscaleRevert();
   }
 
   // Calculate window buffer size

libs/hardware/SDCardManager/include/SDCardManager.h

@@ -29,6 +29,7 @@ class SDCardManager {
   bool exists(const char* path) { return sd.exists(path); }
   bool remove(const char* path) { return sd.remove(path); }
   bool rmdir(const char* path) { return sd.rmdir(path); }
+  bool rename(const char* oldPath, const char* newPath) { return sd.rename(oldPath, newPath); }
 
   bool openFileForRead(const char* moduleName, const char* path, FsFile& file);
   bool openFileForRead(const char* moduleName, const std::string& path, FsFile& file);