feat: Back on home menu opens the most recent book (#2619)

Co-authored-by: kira <rammah@tuta.io>

lib/I18n/translations/english.yaml

@@ -10,6 +10,7 @@ STR_BROWSE_FILES: "Browse Files"
 STR_FILE_TRANSFER: "File Transfer"
 STR_SETTINGS_TITLE: "Settings"
 STR_CONTINUE_READING: "Continue Reading"
+STR_RESUME: "Resume"
 STR_NO_OPEN_BOOK: "No open book"
 STR_START_READING: "Start reading below"
 STR_NO_FILES_FOUND: "No files found"

src/activities/home/HomeActivity.cpp

@@ -179,6 +179,17 @@ void HomeActivity::loop() {
     requestUpdate();
   });
 
+  if (mappedInput.wasPressed(MappedInputManager::Button::Back)) backPressSeen = true;
+
+  // Back is otherwise unused on the home menu: open the most recently read
+  // book directly (recentBooks is most-recent-first and already pruned of
+  // files missing from the SD card). backPressSeen guards against the stale
+  // release of the Back press that closed the previous activity.
+  if (mappedInput.wasReleased(MappedInputManager::Button::Back) && backPressSeen && !recentBooks.empty()) {
+    onSelectBook(recentBooks[0].path);
+    return;
+  }
+
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
     if (selectorIndex < recentBooks.size()) {
       onSelectBook(recentBooks[selectorIndex].path);
@@ -256,7 +267,8 @@ void HomeActivity::render(RenderLock&&) {
       [&menuItems](int index) { return std::string(menuItems[index]); },
       [&menuIcons](int index) { return menuIcons[index]; });
 
-  const auto labels = mappedInput.mapLabels("", tr(STR_SELECT), tr(STR_DIR_UP), tr(STR_DIR_DOWN));
+  const auto labels = mappedInput.mapLabels(recentBooks.empty() ? "" : tr(STR_RESUME), tr(STR_SELECT), tr(STR_DIR_UP),
+                                            tr(STR_DIR_DOWN));
   GUI.drawButtonHints(renderer, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
 
   renderer.displayBuffer();

src/activities/home/HomeActivity.h

@@ -18,6 +18,9 @@ class HomeActivity final : public Activity {
   bool hasOpdsServers = false;
   bool coverRendered = false;      // Track if cover has been rendered once
   bool coverBufferStored = false;  // Track if cover buffer is stored
+  // Home can be entered while Back is still held (e.g. leaving Settings with
+  // Back): ignore that stale release until a fresh press is seen here.
+  bool backPressSeen = false;
   uint8_t* coverBuffer = nullptr;  // HomeActivity's own buffer for cover image
   size_t coverBufferSize = 0;      // Bytes allocated to coverBuffer
   // Logical rect last passed to drawRecentBookCover. The cover snapshot only