feat: implement /rewind command (#15720)

packages/cli/src/ui/AppContainer.tsx

@@ -692,6 +692,7 @@ Logging in with Google... Restarting Gemini CLI to continue.
       toggleDebugProfiler,
       dispatchExtensionStateUpdate,
       addConfirmUpdateExtensionRequest,
+      setText: (text: string) => buffer.setText(text),
     }),
     [
       setAuthState,
@@ -708,6 +709,7 @@ Logging in with Google... Restarting Gemini CLI to continue.
       openPermissionsDialog,
       addConfirmUpdateExtensionRequest,
       toggleDebugProfiler,
+      buffer,
     ],
   );