refactored broad range of the application, split files, modularized calendar and file views, centralized bottom sheets and clipboard handling, and implemented unit test coverage

lib/extensions/text.dart

@@ -10,3 +10,11 @@ extension TextExt on Text {
     return textPainter.size;
   }
 }
+
+/// Returns the first non-empty (after trim) entry, or '' if none match.
+String firstNonEmpty(List<String?> values) {
+  for (final v in values) {
+    if (v != null && v.trim().isNotEmpty) return v;
+  }
+  return '';
+}