Add chapter select support to XTC files (#145)

## Summary

- **What is the goal of this PR?** Add chapter selection support to the
XTC reader activity, including parsing chapter metadata from XTC files.
- **What changes are included?** Implemented XTC chapter parsing and
exposure in the XTC library, added a chapter selection activity for XTC,
integrated it into XtcReaderActivity, and normalized chapter page
indices by shifting them to 0-based.

  ## Additional Context

- The reader uses 0-based page indexing (first page = 0), but the XTC
chapter table appears to be 1-based (first page = 1), so chapter
start/end pages are shifted down by 1 during parsing.

lib/Xtc/Xtc.h

@@ -9,6 +9,7 @@
 
 #include <memory>
 #include <string>
+#include <vector>
 
 #include "Xtc/XtcParser.h"
 #include "Xtc/XtcTypes.h"
@@ -55,6 +56,8 @@ class Xtc {
 
   // Metadata
   std::string getTitle() const;
+  bool hasChapters() const;
+  const std::vector<xtc::ChapterInfo>& getChapters() const;
 
   // Cover image support (for sleep screen)
   std::string getCoverBmpPath() const;