Unfortunately the Google Camera app does not natively support saving pictures/videos/panoramas to SD Card. I am guessing that this goes with Google's general stance against SD cards in general. If your device is not rooted, you are stuck with having to manually move the images/videos.
For rooted devices, there is a work-around to this limitation. Xposed framework allows various modules to override many stock firmware options without using 3rd-party ROMs. It should also work on custom ROMs, but that isn't "officially" supported by the framework's developer. You will need the Pictures2SD module, which makes all media from various camera apps (including Google Camera) to be automatically saved to the DCIM folder of the SD Card.
Xposed Installer app is not directly available via the Google Play Store, so after rooting your S4 (looks like you are already rooted, since you're running a custom ROM), you will need to allow side-loading of applications via
Settings -> Security -> Unknown sources, download and install the APK from here, and activate it according to these instructions:
Installation of the framework:
- Download the Xposed Installer APK and install it
- Launch the Xposed Installer, go to the "Framework" section and click on "Install/Update"
After that, the installation of modules is pretty straight-forward:
Installation of any modules:
- Download .apk (e.g. via the
builtin repository browser) and install it
- Launch the Xposed Installer
and go to the "Modules" section (you will also get there if you click
on the notification warning you that the module is not enabled yet)
- Enable the module by checking the checkbox