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_win/_deps/boost-subbuild/CMakeFiles/boost-populate.dir/cmake_clean.cmake

@@ -0,0 +1,17 @@
+file(REMOVE_RECURSE
+  "CMakeFiles/boost-populate"
+  "CMakeFiles/boost-populate-complete"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-build"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-configure"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-download"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-install"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-mkdir"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-patch"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-test"
+  "boost-populate-prefix/src/boost-populate-stamp/boost-populate-update"
+)
+
+# Per-language clean rules from dependency scanning.
+foreach(lang )
+  include(CMakeFiles/boost-populate.dir/cmake_clean_${lang}.cmake OPTIONAL)
+endforeach()