feat: responsive compact mail view + folder unread badges

- CompactMailDelegate: card-based view for narrow panels (<420px)
  * Avatar with hash-based color, sender + date (relative format)
  * Subject line with attachment icon
  * Action buttons: flag, delete, category, more (context menu)
  * Unread highlight with light blue background + bold sender
- MailListView: automatic switch between tree/table (wide) and list/cards (narrow)
  * QStackedWidget with QTreeView + QListView sharing same proxy model
  * resizeEvent threshold at 420px
  * Signals forwarded to MainMainWindow for actions
- FolderTreeDelegate: custom paint for folder tree
  * Unread count badge (blue pill) right-aligned on folder nodes
  * Account nodes bold, folder nodes normal weight
  * Proper indentation per depth level
- MailItemDao::countUnreadByFolderId() for real-time unread counts
- MainMainWindow handlers for compact actions (flag, delete, category, more menu)

build/CMakeFiles/test_mimestorage_autogen.dir/cmake_clean.cmake

@@ -0,0 +1,10 @@
+file(REMOVE_RECURSE
+  "CMakeFiles/test_mimestorage_autogen"
+  "test_mimestorage_autogen/mocs_compilation.cpp"
+  "test_mimestorage_autogen/timestamp"
+)
+
+# Per-language clean rules from dependency scanning.
+foreach(lang )
+  include(CMakeFiles/test_mimestorage_autogen.dir/cmake_clean_${lang}.cmake OPTIONAL)
+endforeach()