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/EpubReaderChapterSelectionActivity.h

@@ -6,36 +6,59 @@
 
 #include <memory>
 
-#include "../Activity.h"
+#include "../ActivityWithSubactivity.h"
 
-class EpubReaderChapterSelectionActivity final : public Activity {
+class EpubReaderChapterSelectionActivity final : public ActivityWithSubactivity {
   std::shared_ptr<Epub> epub;
+  std::string epubPath;
   TaskHandle_t displayTaskHandle = nullptr;
   SemaphoreHandle_t renderingMutex = nullptr;
   int currentSpineIndex = 0;
+  int currentPage = 0;
+  int totalPagesInSpine = 0;
   int selectorIndex = 0;
   bool updateRequired = false;
   const std::function<void()> onGoBack;
   const std::function<void(int newSpineIndex)> onSelectSpineIndex;
+  const std::function<void(int newSpineIndex, int newPage)> onSyncPosition;
 
   // Number of items that fit on a page, derived from logical screen height.
   // This adapts automatically when switching between portrait and landscape.
   int getPageItems() const;
 
+  // Total items including sync options (top and bottom)
+  int getTotalItems() const;
+
+  // Check if sync option is available (credentials configured)
+  bool hasSyncOption() const;
+
+  // Check if given item index is a sync option (first or last)
+  bool isSyncItem(int index) const;
+
+  // Convert item index to TOC index (accounting for top sync option offset)
+  int tocIndexFromItemIndex(int itemIndex) const;
+
   static void taskTrampoline(void* param);
   [[noreturn]] void displayTaskLoop();
   void renderScreen();
+  void launchSyncActivity();
 
  public:
   explicit EpubReaderChapterSelectionActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
-                                              const std::shared_ptr<Epub>& epub, const int currentSpineIndex,
-                                              const std::function<void()>& onGoBack,
-                                              const std::function<void(int newSpineIndex)>& onSelectSpineIndex)
-      : Activity("EpubReaderChapterSelection", renderer, mappedInput),
+                                              const std::shared_ptr<Epub>& epub, const std::string& epubPath,
+                                              const int currentSpineIndex, const int currentPage,
+                                              const int totalPagesInSpine, const std::function<void()>& onGoBack,
+                                              const std::function<void(int newSpineIndex)>& onSelectSpineIndex,
+                                              const std::function<void(int newSpineIndex, int newPage)>& onSyncPosition)
+      : ActivityWithSubactivity("EpubReaderChapterSelection", renderer, mappedInput),
         epub(epub),
+        epubPath(epubPath),
         currentSpineIndex(currentSpineIndex),
+        currentPage(currentPage),
+        totalPagesInSpine(totalPagesInSpine),
         onGoBack(onGoBack),
-        onSelectSpineIndex(onSelectSpineIndex) {}
+        onSelectSpineIndex(onSelectSpineIndex),
+        onSyncPosition(onSyncPosition) {}
   void onEnter() override;
   void onExit() override;
   void loop() override;