style: fix all cppcheck warnings

- Fix ignored return value in TxtReaderActivity
- Remove unused variables across multiple files
- Add const correctness to DictionaryMargins and EpubReaderActivity
- Replace inefficient substr patterns with resize+append
- Use STL algorithms (find_if, any_of, copy_if, transform) where applicable
- Remove dead sync placeholder code in EpubReaderChapterSelectionActivity
- Add cppcheck suppression for ValueFlow analysis limitation

Resolves all low, medium, and high severity cppcheck defects.

src/activities/reader/EpubReaderActivity.cpp

@@ -386,9 +386,7 @@ void EpubReaderActivity::loop() {
         [this](QuickMenuAction action) {
           // Cache values before exitActivity
           EpubReaderActivity* self = this;
-          GfxRenderer& cachedRenderer = renderer;
-          MappedInputManager& cachedMappedInput = mappedInput;
-          Section* cachedSection = section.get();
+          const Section* cachedSection = section.get();
           SemaphoreHandle_t cachedMutex = renderingMutex;
           
           exitActivity();
@@ -938,7 +936,8 @@ void EpubReaderActivity::renderEndOfBookPrompt() {
   // Book title (truncated if needed)
   std::string bookTitle = epub->getTitle();
   if (bookTitle.length() > 30) {
-    bookTitle = bookTitle.substr(0, 27) + "...";
+    bookTitle.resize(27);
+    bookTitle += "...";
   }
   renderer.drawCenteredText(UI_10_FONT_ID, 120, bookTitle.c_str());
 

src/activities/reader/EpubReaderChapterSelectionActivity.cpp

@@ -10,7 +10,12 @@ namespace {
 constexpr int SKIP_PAGE_MS = 700;
 }  // namespace
 
-bool EpubReaderChapterSelectionActivity::hasSyncOption() const { return false; }
+// Sync feature is currently disabled - will be enabled when implemented
+// NOLINTNEXTLINE(readability-convert-member-functions-to-static)
+bool EpubReaderChapterSelectionActivity::hasSyncOption() const {
+  // TODO: Return true when sync credentials are configured
+  return false;
+}
 
 int EpubReaderChapterSelectionActivity::getTotalItems() const {
   // Add 2 for sync options (top and bottom) if credentials are configured
@@ -18,12 +23,6 @@ int EpubReaderChapterSelectionActivity::getTotalItems() const {
   return epub->getTocItemsCount() + syncCount;
 }
 
-bool EpubReaderChapterSelectionActivity::isSyncItem(int index) const {
-  if (!hasSyncOption()) return false;
-  // First item and last item are sync options
-  return index == 0 || index == getTotalItems() - 1;
-}
-
 int EpubReaderChapterSelectionActivity::tocIndexFromItemIndex(int itemIndex) const {
   // Account for the sync option at the top
   const int offset = hasSyncOption() ? 1 : 0;
@@ -94,10 +93,6 @@ void EpubReaderChapterSelectionActivity::onExit() {
   renderingMutex = nullptr;
 }
 
-void EpubReaderChapterSelectionActivity::launchSyncActivity() {
-  // KOReader sync functionality removed
-}
-
 void EpubReaderChapterSelectionActivity::loop() {
   if (subActivity) {
     subActivity->loop();
@@ -114,13 +109,7 @@ void EpubReaderChapterSelectionActivity::loop() {
   const int totalItems = getTotalItems();
 
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
-    // Check if sync option is selected (first or last item)
-    if (isSyncItem(selectorIndex)) {
-      launchSyncActivity();
-      return;
-    }
-
-    // Get TOC index (account for top sync offset)
+    // Get TOC index (account for top sync offset if enabled)
     const int tocIndex = tocIndexFromItemIndex(selectorIndex);
     const auto newSpineIndex = epub->getSpineIndexForTocIndex(tocIndex);
     if (newSpineIndex == -1) {
@@ -182,19 +171,13 @@ void EpubReaderChapterSelectionActivity::renderScreen() {
     const int displayY = 60 + bezelTop + (itemIndex % pageItems) * 30;
     const bool isSelected = (itemIndex == selectorIndex);
 
-    if (isSyncItem(itemIndex)) {
-      // Draw sync option (at top or bottom)
-      renderer.drawText(UI_10_FONT_ID, 20 + bezelLeft, displayY, ">> Sync Progress", !isSelected);
-    } else {
-      // Draw TOC item (account for top sync offset)
-      const int tocIndex = tocIndexFromItemIndex(itemIndex);
-      auto item = epub->getTocItem(tocIndex);
-      const int indentSize = 20 + bezelLeft + (item.level - 1) * 15;
-      const std::string chapterName =
-          renderer.truncatedText(UI_10_FONT_ID, item.title.c_str(), pageWidth - 40 - bezelLeft - bezelRight - indentSize + 20 + bezelLeft);
-      renderer.drawText(UI_10_FONT_ID, indentSize, 60 + bezelTop + (tocIndex % pageItems) * 30, chapterName.c_str(),
-                        tocIndex != selectorIndex);
-    }
+    // Draw TOC item
+    const int tocIndex = tocIndexFromItemIndex(itemIndex);
+    auto item = epub->getTocItem(tocIndex);
+    const int indentSize = 20 + bezelLeft + (item.level - 1) * 15;
+    const std::string chapterName =
+        renderer.truncatedText(UI_10_FONT_ID, item.title.c_str(), pageWidth - 40 - bezelLeft - bezelRight - indentSize + 20 + bezelLeft);
+    renderer.drawText(UI_10_FONT_ID, indentSize, displayY, chapterName.c_str(), !isSelected);
   }
 
   const auto labels = mappedInput.mapLabels("« Back", "Select", "Up", "Down");

src/activities/reader/EpubReaderChapterSelectionActivity.h

@@ -30,18 +30,15 @@ class EpubReaderChapterSelectionActivity final : public ActivityWithSubactivity
   int getTotalItems() const;
 
   // Check if sync option is available (credentials configured)
+  // Note: Currently always returns false - placeholder for future sync feature
   bool hasSyncOption() const;
 
-  // Check if given item index is a sync option (first or last)
-  bool isSyncItem(int index) const;
-
   // Convert item index to TOC index (accounting for top sync option offset)
   int tocIndexFromItemIndex(int itemIndex) const;
 
   static void taskTrampoline(void* param);
   [[noreturn]] void displayTaskLoop();
   void renderScreen();
-  void launchSyncActivity();
 
  public:
   explicit EpubReaderChapterSelectionActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,

src/activities/reader/TxtReaderActivity.cpp

@@ -88,7 +88,7 @@ void TxtReaderActivity::onEnter() {
     renderer.displayBuffer(EInkDisplay::FAST_REFRESH);
 
     // Generate covers with progress callback
-    txt->generateAllCovers([&](int percent) {
+    (void)txt->generateAllCovers([&](int percent) {
       const unsigned long now = millis();
       if ((now - lastUpdate) >= 3000) {
         lastUpdate = now;
@@ -888,7 +888,8 @@ void TxtReaderActivity::renderEndOfBookPrompt() {
     filename = filename.substr(lastSlash + 1);
   }
   if (filename.length() > 30) {
-    filename = filename.substr(0, 27) + "...";
+    filename.resize(27);
+    filename += "...";
   }
   renderer.drawCenteredText(UI_10_FONT_ID, 120, filename.c_str());