fix: placeholder cover text, indexing timing, TOC long-press, cache deletion UI

- Fix fp4 fixed-point misuse in PlaceholderCoverGenerator (advanceX is 12.4
  fixed-point, not pixels) causing only first letter of each word to render
- Remove duplicate silentIndexNextChapterIfNeeded() call from loop() that
  blocked UI before render, preventing the indexing indicator from showing
- Fix indexing icon Y position to align within the status bar
- Add ignoreNextConfirmRelease to EpubReaderChapterSelectionActivity so
  long-press confirm release doesn't immediately select the first TOC item
- Reload recent books after cache deletion in HomeActivity and clear stale
  ignoreNextConfirmRelease flag to fix "no open books" and double-press bugs

Made-with: Cursor

src/activities/home/HomeActivity.cpp

@@ -307,6 +307,7 @@ void HomeActivity::openManageMenu(const std::string& bookPath) {
   startActivityForResult(
       std::make_unique<BookManageMenuActivity>(renderer, mappedInput, capturedPath, isArchived, true),
       [this, capturedPath](const ActivityResult& result) {
+        ignoreNextConfirmRelease = false;
         if (result.isCancelled) {
           requestUpdate();
           return;
@@ -339,13 +340,13 @@ void HomeActivity::openManageMenu(const std::string& bookPath) {
           GUI.drawPopup(renderer, success ? tr(STR_DONE) : tr(STR_ACTION_FAILED));
         }
         requestUpdateAndWait();
-        recentBooks.clear();
         recentsLoaded = false;
         recentsLoading = false;
         coverRendered = false;
         freeCoverBuffer();
         selectorIndex = 0;
         firstRenderDone = false;
+        loadRecentBooks(UITheme::getInstance().getMetrics().homeRecentBooksCount);
         requestUpdate();
       });
 }