feat: fai_dart_sdk scaffold

Dart package skeleton for the F∆I gRPC client. Used by F∆I
Studio (Tier-2) and Tier-3 domain apps (DigiScout / J∆I /
Scout). Public surface — HubClient, HubEndpoint — is committed
as a typed stub so downstream apps can compile against it
immediately. Generated proto bindings land in a follow-up
commit once the codegen step (planned: tools/generate.sh
wrapping protoc-gen-dart against ../fai_platform/proto) is
wired in.

Future Forgejo path: fai/dart-sdk.

dart analyze: clean. dart test: 4/4.

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

analysis_options.yaml

@@ -0,0 +1,30 @@
+# This file configures the static analysis results for your project (errors,
+# warnings, and lints).
+#
+# This enables the 'recommended' set of lints from `package:lints`.
+# This set helps identify many issues that may lead to problems when running
+# or consuming Dart code, and enforces writing Dart using a single, idiomatic
+# style and format.
+#
+# If you want a smaller set of lints you can change this to specify
+# 'package:lints/core.yaml'. These are just the most critical lints
+# (the recommended set includes the core lints).
+# The core lints are also what is used by pub.dev for scoring packages.
+
+include: package:lints/recommended.yaml
+
+# Uncomment the following section to specify additional rules.
+
+# linter:
+#   rules:
+#     - camel_case_types
+
+# analyzer:
+#   exclude:
+#     - path/to/excluded/files/**
+
+# For more information about the core and recommended set of lints, see
+# https://dart.dev/go/core-lints
+
+# For additional information about configuring this file, see
+# https://dart.dev/guides/language/analysis-options