Add touch-down and long-press input detection

Implement touch-down event detection to provide immediate visual feedback when touching list items, mirroring button navigation behavior. Add long-press detection (500ms threshold) to distinguish between tap and hold gestures. Apply touch-down selection updates to file browser, home menu, and recent books activities.

src/activities/home/FileBrowserActivity.cpp

@@ -206,6 +206,14 @@ void FileBrowserActivity::loop() {
   const int pathReserved = renderer.getLineHeight(SMALL_FONT_ID) + UITheme::getInstance().getMetrics().verticalSpacing;
   const int pageItems = UITheme::getNumberOfItemsPerPage(renderer, true, false, true, false, pathReserved);
 
+  // Touch-down moves the selector to the pressed entry (shows selected state); release
+  // opens it below.
+  int downId = -1;
+  if (mappedInput.wasItemTouchedDown(downId) && downId >= 0 && downId < static_cast<int>(files.size())) {
+    selectorIndex = downId;
+    requestUpdate();
+  }
+
   // A tap opens the tapped entry (held-time is 0 on a tap, so it takes the short-press
   // open path below, never the long-press delete).
   int tappedId = -1;

src/activities/home/HomeActivity.cpp

@@ -183,6 +183,14 @@ void HomeActivity::loop() {
   // menu-local ids (it is drawn with selectorIndex offset by recentBooks.size()),
   // so map the tapped id back into the global selector space. (The recent-book
   // cover is a separate, single-item draw path — tappable in a later phase.)
+  // Touch-down moves the selector to the pressed menu button (shows selected state),
+  // like Up/Down; release opens it below.
+  int downId = -1;
+  if (mappedInput.wasItemTouchedDown(downId)) {
+    selectorIndex = static_cast<int>(recentBooks.size()) + downId;
+    requestUpdate();
+  }
+
   int tappedId = -1;
   const bool tapped = mappedInput.wasItemTapped(tappedId);
   if (tapped) {

src/activities/home/RecentBooksActivity.cpp

@@ -63,6 +63,12 @@ void RecentBooksActivity::loop() {
     return;
   }
 
+  int downId = -1;
+  if (mappedInput.wasItemTouchedDown(downId) && downId >= 0 && downId < static_cast<int>(recentBooks.size())) {
+    selectorIndex = downId;
+    requestUpdate();
+  }
+
   int tappedId = -1;
   const bool tapped = mappedInput.wasItemTapped(tappedId);
   if (tapped && tappedId >= 0 && tappedId < static_cast<int>(recentBooks.size())) selectorIndex = tappedId;