fix: show "Failed to index" when failing to parse epub (#2556)

src/activities/reader/EpubReaderActivity.h

@@ -32,6 +32,10 @@ class EpubReaderActivity final : public Activity {
   float pendingSpineProgress = 0.0f;
   bool pendingScreenshot = false;
   bool pendingSyncSaveError = false;
+  // Consecutive page-load failures. Each failure drops the section and rebuilds on the next render,
+  // which recovers a transiently corrupt cache; capped so a persistently bad page can't spin forever.
+  uint8_t pageLoadRetryCount = 0;
+  static constexpr uint8_t MAX_PAGE_LOAD_RETRIES = 3;
   bool skipNextButtonCheck = false;  // Skip button processing for one frame after subactivity exit
   bool automaticPageTurnActive = false;
   bool showBookmarkMessage = false;