feat(ui): change popup logic (#442)

## Summary

* refactors Indexing popups into ScreenComponents (they had different
implementations in different files)
* removes Indexing popup for small chapters
* only show Indexing popup (without progress bar) for large chapters
(using same minimum file size condition as for progress bar before)

## Additional Context

* Having to show even single popup message and redraw the screen slows
down the flow significantly
* Testing results:
    * Opening large chapter with progress bar - 11 seconds
* Same chapter without progress bar, only single Indexing popup - 5
seconds

---

### AI Usage

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

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -10,8 +10,8 @@
 const char* HEADER_TAGS[] = {"h1", "h2", "h3", "h4", "h5", "h6"};
 constexpr int NUM_HEADER_TAGS = sizeof(HEADER_TAGS) / sizeof(HEADER_TAGS[0]);
 
-// Minimum file size (in bytes) to show progress bar - smaller chapters don't benefit from it
-constexpr size_t MIN_SIZE_FOR_PROGRESS = 50 * 1024;  // 50KB
+// Minimum file size (in bytes) to show indexing popup - smaller chapters don't benefit from it
+constexpr size_t MIN_SIZE_FOR_POPUP = 50 * 1024;  // 50KB
 
 const char* BLOCK_TAGS[] = {"p", "li", "div", "br", "blockquote"};
 constexpr int NUM_BLOCK_TAGS = sizeof(BLOCK_TAGS) / sizeof(BLOCK_TAGS[0]);
@@ -289,10 +289,10 @@ bool ChapterHtmlSlimParser::parseAndBuildPages() {
     return false;
   }
 
-  // Get file size for progress calculation
-  const size_t totalSize = file.size();
-  size_t bytesRead = 0;
-  int lastProgress = -1;
+  // Get file size to decide whether to show indexing popup.
+  if (popupFn && file.size() >= MIN_SIZE_FOR_POPUP) {
+    popupFn();
+  }
 
   XML_SetUserData(parser, this);
   XML_SetElementHandler(parser, startElement, endElement);
@@ -322,17 +322,6 @@ bool ChapterHtmlSlimParser::parseAndBuildPages() {
       return false;
     }
 
-    // Update progress (call every 10% change to avoid too frequent updates)
-    // Only show progress for larger chapters where rendering overhead is worth it
-    bytesRead += len;
-    if (progressFn && totalSize >= MIN_SIZE_FOR_PROGRESS) {
-      const int progress = static_cast<int>((bytesRead * 100) / totalSize);
-      if (lastProgress / 10 != progress / 10) {
-        lastProgress = progress;
-        progressFn(progress);
-      }
-    }
-
     done = file.available() == 0;
 
     if (XML_ParseBuffer(parser, static_cast<int>(len), done) == XML_STATUS_ERROR) {