You say "I know for a fact that the application will never need a client/server architecture" but also talk about a "Production Website" - surely a website will

You say "I know for a fact that the application will never need a client/server architecture" but also talk about a "Production Website" - surely a website will by definition need a client-server architecture? SQLite will probably suffice, so long as you aren't running very complex queries. SQlite has some documentation on its concurrency model - https://www.sqlite.org/lockingv3.html https://www.sqlite.org/lockingv3.html. You might also want to look at https://www.sqlite.org/wal.html https://www.sqlite.org/wal.html.