feat: F∆I Studio MVP scaffold (Tier-2 desktop GUI)

Initial scaffold for the F∆I Platform Tier-2 generic GUI client.
Flutter Desktop (macOS, Linux, Windows). Three MVP pages with
mock data, sharing one navigation shell:

- Modules — installed modules with capabilities, declared
  permissions and required services.
- Audit — event-stream view with type filter and tone-coded
  rows (started / completed / failed).
- Approvals — pending system.approval@^0 reviews with prompt,
  payload preview, and approve/reject buttons.

Live gRPC connection arrives in the next iteration via
fai_dart_sdk (sibling repo, currently a typed stub).

Future Forgejo path: fai/studio. Local layout matches existing
fai_platform/ convention.

Background: see docs/architecture/client.md in the platform
repo. The tier-2 client was previously called "Stage" — renamed
to "Studio" on 2026-05-05 to avoid confusion with
"staging environment".

flutter analyze: clean. flutter test: 2/2.

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

pubspec.yaml

@@ -0,0 +1,24 @@
+name: fai_studio
+description: "F∆I Studio — desktop GUI for the F∆I hub"
+publish_to: 'none'
+version: 0.1.0
+
+environment:
+  sdk: ^3.11.0-200.1.beta
+
+dependencies:
+  flutter:
+    sdk: flutter
+  cupertino_icons: ^1.0.8
+
+  # Sibling package; will move to Forgejo path once published.
+  fai_dart_sdk:
+    path: ../fai_dart_sdk
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^6.0.0
+
+flutter:
+  uses-material-design: true