feat(app): cycle agent modes with Shift+Tab

packages/app/src/composer/keyboard-scope.tsx

@@ -0,0 +1,31 @@
+import {
+  createContext,
+  useContext,
+  useMemo,
+  type PropsWithChildren,
+  type ReactElement,
+} from "react";
+
+interface ComposerKeyboardScopeValue {
+  isActiveComposer: boolean;
+}
+
+const ComposerKeyboardScopeContext = createContext<ComposerKeyboardScopeValue>({
+  isActiveComposer: false,
+});
+
+export function ComposerKeyboardScopeProvider({
+  isActiveComposer,
+  children,
+}: PropsWithChildren<ComposerKeyboardScopeValue>): ReactElement {
+  const value = useMemo(() => ({ isActiveComposer }), [isActiveComposer]);
+  return (
+    <ComposerKeyboardScopeContext.Provider value={value}>
+      {children}
+    </ComposerKeyboardScopeContext.Provider>
+  );
+}
+
+export function useComposerKeyboardScope(): ComposerKeyboardScopeValue {
+  return useContext(ComposerKeyboardScopeContext);
+}