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/EpubReaderActivity.h

@@ -24,6 +24,9 @@ class EpubReaderActivity final : public Activity {
   bool pendingPercentJump = false;
   // Normalized 0.0-1.0 progress within the target spine item, computed from book percentage.
   float pendingSpineProgress = 0.0f;
+  // Pending paragraph index from KOReader sync (resolved to page via Section paragraph LUT)
+  bool pendingParagraphLookup = false;
+  uint16_t pendingParagraphIndex = 0;
   bool pendingScreenshot = false;
   bool skipNextButtonCheck = false;  // Skip button processing for one frame after subactivity exit
   bool automaticPageTurnActive = false;