build(ground-suite): add a separate pinned Flutter shell

Provide a separate Flutter development shell from the existing locked
Nix input and document the application build commands.

Validation: locked environment/version probe; no native application
qualification is claimed.

ground_suite/README.md

@@ -1,21 +1,41 @@
 # Kaptan Ground Suite
 
+## Environment
+
+From the repository root, optionally enter the app development shell pinned by
+`flake.lock`:
+
+```sh
+nix develop .#ground-suite
+```
+
+This shell supplies Flutter 3.41.9, Dart 3.11.5 and Linux desktop build
+dependencies. The default firmware shell does not include these tools.
+
 ## Run
 
+From the repository root, in that shell or an equivalent Flutter environment:
+
 ```sh
 cd ground_suite
-flutter pub get
+flutter pub get --enforce-lockfile
 flutter run -d linux
 ```
 
-On NixOS, enter `nix shell nixpkgs#flutter` first.
-For web, use `flutter run -d chrome`.
+For web, run `flutter run -d chrome` from `ground_suite/` with Chrome available.
 
 ## Check
 
+Run from `ground_suite/` after the locked dependency fetch above:
+
 ```sh
 dart format --output=none --set-exit-if-changed lib
-flutter analyze
-flutter build web
-flutter build linux
+dart analyze
+flutter analyze --no-pub
+flutter build web --release --no-pub
+flutter build linux --release --no-pub
 ```
+
+There is currently no `test/` directory or widget test suite. Web and Linux
+builds do not verify the Windows or macOS runners. See the central
+[development guide](../docs/src/development.md#ground-suite-builds).