chore: rename package + dir + repo to fai_client_sdk

Adopts the three SDK families convention from
fai/platform/docs/architecture/sdks.md — base name carries
the family, language suffix on dir + repo only:

  fai_dart_sdk          (pkg) → fai_client_sdk
  fai_dart_sdk          (dir) → fai_client_sdk_dart
  fai/dart-sdk          (repo) → fai/client-sdk-dart

Internal lib/test/example file renames track the package
name. Old git.flemming.ws URL also retired here.

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

example/fai_client_sdk_example.dart

@@ -0,0 +1,18 @@
+// Example: connect to a locally-running F∆I hub.
+//
+// Run with `dart run example/fai_client_sdk_example.dart`.
+
+import 'package:fai_client_sdk/fai_client_sdk.dart';
+
+Future<void> main() async {
+  final client = HubClient(
+    endpoint: const HubEndpoint(host: '127.0.0.1', port: 50051),
+  );
+
+  // ignore: avoid_print
+  print('would connect to ${client.endpoint}');
+  // ignore: avoid_print
+  print('(SDK is a stub today; live RPC arrives with codegen)');
+
+  await client.close();
+}