add option for offline / self hotspots in SBC

Description
It would be good to have option where I want the system to be self contained. Once the image is installed in pi and booted, it starts a wifi hotspot, and once connected to the hotspot we can go to a domain where nextcloud is setup.
It is very useful in cases where I want the whole system with me on the go, without internet. Everything is contained within the sd card. With server side encryption, it becomes a great small cloud alternative. Ofcourse any function that requires Internet to function should be disabled by default, or can be left as it is with the understanding that it won't work.

Example
The idea is based on moodlebox -- moodlebox.net, which sets up moodle in this form, and can be used without internet anywhere.

The issue names no files, tests, or entry points; begin by tracing how the Raspberry Pi image boots and configures networking. Define the offline hotspot and Nextcloud access flow, including the expected behavior of Internet-dependent functions. Done means the system operates self-contained from the SD card without Internet access.