fix: small QoL: return to the last selected menu location (#1629)

## Summary

* **What is the goal of this PR?** Small UX improvement to the Home
screen by preserving the last selected cursor position when returning to
it.

It supersedes #985 and #1103, which are both significantly outdated and
hundreds of commits behind master.

---

### AI Usage

Did you use AI tools to help write this code? _**< YES >**_

src/activities/home/HomeActivity.cpp

@@ -113,11 +113,12 @@ void HomeActivity::onEnter() {
 
   hasOpdsServers = OPDS_STORE.hasServers();
 
-  selectorIndex = 0;
-
   const auto& metrics = UITheme::getInstance().getMetrics();
   loadRecentBooks(metrics.homeRecentBooksCount);
 
+  const auto base = static_cast<int>(recentBooks.size());
+  selectorIndex = initialMenuItem == HomeMenuItem::NONE ? 0 : base + menuItemToIndex(initialMenuItem, hasOpdsServers);
+
   // Trigger first update
   requestUpdate();
 }
@@ -179,27 +180,29 @@ void HomeActivity::loop() {
   });
 
   if (mappedInput.wasReleased(MappedInputManager::Button::Confirm)) {
-    // Calculate dynamic indices based on which options are available
-    int idx = 0;
-    int menuSelectedIndex = selectorIndex - static_cast<int>(recentBooks.size());
-    const int fileBrowserIdx = idx++;
-    const int recentsIdx = idx++;
-    const int opdsLibraryIdx = hasOpdsServers ? idx++ : -1;
-    const int fileTransferIdx = idx++;
-    const int settingsIdx = idx;
-
     if (selectorIndex < recentBooks.size()) {
       onSelectBook(recentBooks[selectorIndex].path);
-    } else if (menuSelectedIndex == fileBrowserIdx) {
-      onFileBrowserOpen();
-    } else if (menuSelectedIndex == recentsIdx) {
-      onRecentsOpen();
-    } else if (menuSelectedIndex == opdsLibraryIdx) {
-      onOpdsBrowserOpen();
-    } else if (menuSelectedIndex == fileTransferIdx) {
-      onFileTransferOpen();
-    } else if (menuSelectedIndex == settingsIdx) {
-      onSettingsOpen();
+    } else {
+      const int menuIndex = selectorIndex - static_cast<int>(recentBooks.size());
+      switch (indexToMenuItem(menuIndex, hasOpdsServers)) {
+        case HomeMenuItem::FILE_BROWSER:
+          onFileBrowserOpen();
+          break;
+        case HomeMenuItem::RECENTS:
+          onRecentsOpen();
+          break;
+        case HomeMenuItem::OPDS_BROWSER:
+          onOpdsBrowserOpen();
+          break;
+        case HomeMenuItem::FILE_TRANSFER:
+          onFileTransferOpen();
+          break;
+        case HomeMenuItem::SETTINGS_MENU:
+          onSettingsOpen();
+          break;
+        default:
+          break;
+      }
     }
   }
 }

src/activities/home/HomeActivity.h

@@ -28,6 +28,33 @@ class HomeActivity final : public Activity {
   int coverRectW = 0;
   int coverRectH = 0;
   std::vector<RecentBook> recentBooks;
+  const HomeMenuItem initialMenuItem;
+
+  // Convert HomeMenuItem to menu index (used in onEnter)
+  static int menuItemToIndex(HomeMenuItem item, bool hasOpdsUrl) {
+    int i = 0;
+    if (item == HomeMenuItem::FILE_BROWSER) return i;
+    ++i;
+    if (item == HomeMenuItem::RECENTS) return i;
+    ++i;
+    if (item == HomeMenuItem::OPDS_BROWSER) return hasOpdsUrl ? i : 0;
+    if (hasOpdsUrl) ++i;
+    if (item == HomeMenuItem::FILE_TRANSFER) return i;
+    ++i;
+    if (item == HomeMenuItem::SETTINGS_MENU) return i;
+    return 0;
+  }
+
+  // Convert menu index to HomeMenuItem (used in loop)
+  static HomeMenuItem indexToMenuItem(int idx, bool hasOpdsUrl) {
+    int i = 0;
+    if (idx == i++) return HomeMenuItem::FILE_BROWSER;
+    if (idx == i++) return HomeMenuItem::RECENTS;
+    if (hasOpdsUrl && idx == i++) return HomeMenuItem::OPDS_BROWSER;
+    if (idx == i++) return HomeMenuItem::FILE_TRANSFER;
+    if (idx == i) return HomeMenuItem::SETTINGS_MENU;
+    return HomeMenuItem::NONE;
+  }
   void onSelectBook(const std::string& path);
   void onFileBrowserOpen();
   void onRecentsOpen();
@@ -43,8 +70,9 @@ class HomeActivity final : public Activity {
   void loadRecentCovers(int coverHeight);
 
  public:
-  explicit HomeActivity(GfxRenderer& renderer, MappedInputManager& mappedInput)
-      : Activity("Home", renderer, mappedInput) {}
+  explicit HomeActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                        HomeMenuItem initialMenuItemValue = HomeMenuItem::NONE)
+      : Activity("Home", renderer, mappedInput), initialMenuItem(initialMenuItemValue) {}
   void onEnter() override;
   void onExit() override;
   void loop() override;