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

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

lib/Epub/Epub.h

@@ -62,5 +62,5 @@ class Epub {
   int getSpineIndexForTextReference() const;
 
   size_t getBookSize() const;
-  uint8_t calculateProgress(int currentSpineIndex, float currentSpineRead) const;
+  float calculateProgress(int currentSpineIndex, float currentSpineRead) const;
 };