Adds KOReader Sync support (#232)

## Summary

- Adds KOReader progress sync integration, allowing CrossPoint to sync
reading positions with other
KOReader-compatible devices
- Stores credentials securely with XOR obfuscation
- Uses KOReader's partial MD5 document hashing for cross-device book
matching
  - Syncs position via percentage with estimated XPath for compatibility

# Features
- Settings: KOReader Username, Password, and Authenticate options
- Sync from chapters menu: "Sync Progress" option appears when
credentials are configured
- Bidirectional sync: Can apply remote progress or upload local progress

---------

Co-authored-by: Dave Allie <dave@daveallie.com>

src/activities/reader/EpubReaderActivity.cpp

@@ -118,9 +118,11 @@ void EpubReaderActivity::loop() {
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
     // Don't start activity transition while rendering
     xSemaphoreTake(renderingMutex, portMAX_DELAY);
+    const int currentPage = section ? section->currentPage : 0;
+    const int totalPages = section ? section->pageCount : 0;
     exitActivity();
     enterNewActivity(new EpubReaderChapterSelectionActivity(
-        this->renderer, this->mappedInput, epub, currentSpineIndex,
+        this->renderer, this->mappedInput, epub, epub->getPath(), currentSpineIndex, currentPage, totalPages,
         [this] {
           exitActivity();
           updateRequired = true;
@@ -133,6 +135,16 @@ void EpubReaderActivity::loop() {
           }
           exitActivity();
           updateRequired = true;
+        },
+        [this](const int newSpineIndex, const int newPage) {
+          // Handle sync position
+          if (currentSpineIndex != newSpineIndex || (section && section->currentPage != newPage)) {
+            currentSpineIndex = newSpineIndex;
+            nextPageNumber = newPage;
+            section.reset();
+          }
+          exitActivity();
+          updateRequired = true;
         }));
     xSemaphoreGive(renderingMutex);
   }
@@ -430,11 +442,13 @@ void EpubReaderActivity::renderStatusBar(const int orientedMarginRight, const in
   if (showProgress) {
     // Calculate progress in book
     const float sectionChapterProg = static_cast<float>(section->currentPage) / section->pageCount;
-    const uint8_t bookProgress = epub->calculateProgress(currentSpineIndex, sectionChapterProg);
+    const float bookProgress = epub->calculateProgress(currentSpineIndex, sectionChapterProg) * 100;
 
     // Right aligned text for progress counter
-    const std::string progress = std::to_string(section->currentPage + 1) + "/" + std::to_string(section->pageCount) +
-                                 "  " + std::to_string(bookProgress) + "%";
+    char progressStr[32];
+    snprintf(progressStr, sizeof(progressStr), "%d/%d  %.1f%%", section->currentPage + 1, section->pageCount,
+             bookProgress);
+    const std::string progress = progressStr;
     progressTextWidth = renderer.getTextWidth(SMALL_FONT_ID, progress.c_str());
     renderer.drawText(SMALL_FONT_ID, renderer.getScreenWidth() - orientedMarginRight - progressTextWidth, textY,
                       progress.c_str());