chore(studio): switch to fai_client_sdk (renamed from fai_dart_sdk)

The Dart SDK package was renamed package: fai_dart_sdk →
fai_client_sdk and the dir + Forgejo repo got a -dart language
suffix per the three SDK families convention in
fai/platform/docs/architecture/sdks.md. Updates the path
dep, dep name, every `package:fai_dart_sdk/...` import, and
the one comment that named the SDK.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/data/friendly_error.dart

@@ -34,7 +34,7 @@ class FriendlyError {
 FriendlyError friendlyError(Object error, AppLocalizations l) {
   // We deliberately don't import package:grpc here so Studio
   // doesn't have to add it to its own pubspec — the dependency
-  // lives one layer down in fai_dart_sdk. `GrpcError` has a
+  // lives one layer down in fai_client_sdk. `GrpcError` has a
   // stable `.code` (int) and `.message` (String?) shape; we
   // duck-type on those instead of an `is` check.
   final code = _intField(error, 'code');