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

pubspec.yaml

@@ -38,6 +38,9 @@ dependencies:
   emoji_picker_flutter: ^4.3.0
   file_picker: ^11.0.2
   filesize: ^2.0.1
+  # Disk cache behind cached_network_image; used directly by the dev tools to
+  # size and empty it. Already present transitively.
+  flutter_cache_manager: ^3.4.1
   firebase_core: ^4.1.0
   firebase_messaging: ^16.0.1
   flutter_app_badge: ^2.0.2