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.

src/activities/reader/XtcReaderChapterSelectionActivity.h

@@ -0,0 +1,41 @@
+#pragma once
+#include <Xtc.h>
+#include <freertos/FreeRTOS.h>
+#include <freertos/semphr.h>
+#include <freertos/task.h>
+
+#include <memory>
+
+#include "../Activity.h"
+
+class XtcReaderChapterSelectionActivity final : public Activity {
+  std::shared_ptr<Xtc> xtc;
+  TaskHandle_t displayTaskHandle = nullptr;
+  SemaphoreHandle_t renderingMutex = nullptr;
+  uint32_t currentPage = 0;
+  int selectorIndex = 0;
+  bool updateRequired = false;
+  const std::function<void()> onGoBack;
+  const std::function<void(uint32_t newPage)> onSelectPage;
+
+  int getPageItems() const;
+  int findChapterIndexForPage(uint32_t page) const;
+
+  static void taskTrampoline(void* param);
+  [[noreturn]] void displayTaskLoop();
+  void renderScreen();
+
+ public:
+  explicit XtcReaderChapterSelectionActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                             const std::shared_ptr<Xtc>& xtc, uint32_t currentPage,
+                                             const std::function<void()>& onGoBack,
+                                             const std::function<void(uint32_t newPage)>& onSelectPage)
+      : Activity("XtcReaderChapterSelection", renderer, mappedInput),
+        xtc(xtc),
+        currentPage(currentPage),
+        onGoBack(onGoBack),
+        onSelectPage(onSelectPage) {}
+  void onEnter() override;
+  void onExit() override;
+  void loop() override;
+};