fix: Switch to xpath map for paragraph level syncing in KOSync (#1686)

Switch KOReader sync progress mapping from chapter matching to
XPath-based mapping.

- resolves KOReader positions using real XHTML ancestry paths
- supports paragraph-based upload mapping with text offsets
where needed
- passes the current paragraph index into sync so uploads map
back to KOReader more accurately

No HTTP client changes are included. No reader-state or resume-flow
changes are included.

---------

Co-authored-by: jpirnay <jens@pirnay.com>

src/activities/reader/EpubReaderActivity.h

@@ -3,6 +3,8 @@
 #include <Epub/FootnoteEntry.h>
 #include <Epub/Section.h>
 
+#include <optional>
+
 #include "EpubReaderMenuActivity.h"
 #include "activities/Activity.h"
 
@@ -11,6 +13,7 @@ class EpubReaderActivity final : public Activity {
   std::unique_ptr<Section> section = nullptr;
   int currentSpineIndex = 0;
   int nextPageNumber = 0;
+  std::optional<uint16_t> pendingPageJump;
   // Set when navigating to a footnote href with a fragment (e.g. #note1).
   // Cleared on the next render after the new section loads and resolves it to a page.
   std::string pendingAnchor;