I'd suggest reconsidering SQLite. It's really robust and not that hard to use, there's tons of libraries and bindings for it in every language. It's probably already incorporated into Electron. And unless you're using Express Edition, you need to use a paid license version of SQL Server.
I'm not up-to-date on the Electron and Angular spaces, but since they are web-based you have some additional surface area that could be compromised. Since this is going to be isolated I don't see how a web programming platform benefits, except for ease of programming. If you're serious about "100% paranoia" then I think you'd be better off with a .Net language or C/C++, something that doesn't already include networking.
If you're air-gapping it and using SQL Server, suggest you disable all the network libraries except for Shared Memory. You'd sacrifice the Dedicated Admin connection though, which requires TCP/IP, but you could probably work around any situation that would require it.
Additionally, you need to figure out something for backing up the database(s), and if you're using TDE or Always Encrypted you also need to back up all the keys and keep them elsewhere. Backing up only on the same laptop is as bad as not backing up at all, so you'd have to have some way to offload the data/backups to other protected storage. Simplest suggestion is a USB drive with enough capacity, and keeping it locked up in a safe.