home screen performance fix

src/activities/home/HomeActivity.h

@@ -15,9 +15,13 @@ class HomeActivity final : public Activity {
   bool hasContinueReading = false;
   bool hasOpdsUrl = false;
   bool hasCoverImage = false;
-  bool coverRendered = false;      // Track if cover has been rendered once
-  bool coverBufferStored = false;  // Track if cover buffer is stored
-  uint8_t* coverBuffer = nullptr;  // HomeActivity's own buffer for cover image
+
+  // Static cover buffer - persists across activity changes to avoid reloading from SD
+  static bool coverRendered;       // Track if cover has been rendered once
+  static bool coverBufferStored;   // Track if cover buffer is stored
+  static uint8_t* coverBuffer;     // HomeActivity's own buffer for cover image
+  static std::string cachedCoverPath;  // Path of the cached cover (to detect book changes)
+
   std::string lastBookTitle;
   std::string lastBookAuthor;
   std::string coverBmpPath;