Add paragraph index LUT for accurate KOReader position sync

Store per-page paragraph indices in section cache to enable precise
XPath-to-page and page-to-XPath mapping without reparsing XHTML.

Forward path (upload): generates XPath directly from paragraph LUT
instead of byte-offset estimation, eliminating drift in chapters
with non-uniform content density.

Reverse path (download): resolves incoming KOReader XPath p[N] to
the exact page via paragraph LUT lookup.

Paragraph counter counts all <p> elements including display:none
to match ChapterXPathIndexer and crengine's standard XPath counting.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/activities/reader/KOReaderSyncActivity.h

@@ -22,13 +22,16 @@ class KOReaderSyncActivity final : public Activity {
  public:
   explicit KOReaderSyncActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
                                 const std::shared_ptr<Epub>& epub, const std::string& epubPath, int currentSpineIndex,
-                                int currentPage, int totalPagesInSpine)
+                                int currentPage, int totalPagesInSpine, uint16_t paragraphIndex = 0,
+                                bool hasParagraphIndex = false)
       : Activity("KOReaderSync", renderer, mappedInput),
         epub(epub),
         epubPath(epubPath),
         currentSpineIndex(currentSpineIndex),
         currentPage(currentPage),
         totalPagesInSpine(totalPagesInSpine),
+        localParagraphIndex(paragraphIndex),
+        hasLocalParagraphIndex(hasParagraphIndex),
         remoteProgress{},
         remotePosition{},
         localProgress{} {}
@@ -57,6 +60,8 @@ class KOReaderSyncActivity final : public Activity {
   int currentSpineIndex;
   int currentPage;
   int totalPagesInSpine;
+  uint16_t localParagraphIndex;
+  bool hasLocalParagraphIndex;
 
   State state = WIFI_SELECTION;
   std::string statusMessage;