feat(studio): Cmd+S / Cmd+Enter shortcuts in flow editor

Wraps the FlowEditorPage in Shortcuts/Actions so
Cmd+S (or Ctrl+S) saves and Cmd+Enter (or Ctrl+Enter) runs
the active flow, no matter whether the code field or
toolbar has focus. Matches the rest of Studio's keyboard-
first ethos.

Disabled when no flow is open or an operation is already
in progress.

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

lib/pages/flow_editor.dart

@@ -253,6 +253,43 @@ outputs:
     final l = AppLocalizations.of(context)!;
     final theme = Theme.of(context);
 
+    // Cmd+S / Ctrl+S → save, Cmd+Enter / Ctrl+Enter → run.
+    // We layer the Shortcuts widget at the page root so the
+    // bindings work whether the editor area has focus or not.
+    final shortcuts = <ShortcutActivator, Intent>{
+      LogicalKeySet(LogicalKeyboardKey.meta, LogicalKeyboardKey.keyS):
+          const _SaveIntent(),
+      LogicalKeySet(LogicalKeyboardKey.control, LogicalKeyboardKey.keyS):
+          const _SaveIntent(),
+      LogicalKeySet(LogicalKeyboardKey.meta, LogicalKeyboardKey.enter):
+          const _RunIntent(),
+      LogicalKeySet(LogicalKeyboardKey.control, LogicalKeyboardKey.enter):
+          const _RunIntent(),
+    };
+
+    return Shortcuts(
+      shortcuts: shortcuts,
+      child: Actions(
+        actions: <Type, Action<Intent>>{
+          _SaveIntent: CallbackAction<_SaveIntent>(
+            onInvoke: (_) {
+              if (_activeName != null && !_saving) _save();
+              return null;
+            },
+          ),
+          _RunIntent: CallbackAction<_RunIntent>(
+            onInvoke: (_) {
+              if (_activeName != null && !_running) _run();
+              return null;
+            },
+          ),
+        },
+        child: Focus(autofocus: true, child: _buildScaffold(l, theme)),
+      ),
+    );
+  }
+
+  Widget _buildScaffold(AppLocalizations l, ThemeData theme) {
     return Scaffold(
       body: Column(
         crossAxisAlignment: CrossAxisAlignment.stretch,
@@ -303,6 +340,14 @@ outputs:
   }
 }
 
+class _SaveIntent extends Intent {
+  const _SaveIntent();
+}
+
+class _RunIntent extends Intent {
+  const _RunIntent();
+}
+
 class _FlowFile {
   final String name;
   final String path;