reworked developer tools with diagnostics, storage viewers and release-capable debug overlays

lib/utils/directory_size.dart

@@ -0,0 +1,16 @@
+import 'dart:io';
+
+/// Total byte size of all files below [dir]; `0` when it doesn't exist or
+/// can't be listed.
+Future<int> directorySize(Directory dir) async {
+  var sum = 0;
+  try {
+    if (!dir.existsSync()) return 0;
+    await for (final entity in dir.list(recursive: true, followLinks: false)) {
+      if (entity is File) sum += await entity.length();
+    }
+  } on FileSystemException {
+    // Files can vanish mid-walk (cache pruning); report what was counted.
+  }
+  return sum;
+}