Share code between database application and SvelteKit application

[ScriptRaccoon]

The repository basically contains two applications: the database application¹ (seed files, seed script, deduction script, etc.) and the SvelteKit application (user interface). The database application lives in /databases, while the SvelteKit application lives in /src. Both have long relied on similar functions and configuration objects, but until now this code was duplicated rather than shared.

This PR resolves this by adding a new /shared folder at the root. Both the database application and the SvelteKit application now import common functions and configuration objects from there. As a notable example, deduction helpers have been extracted that can be used in three places: the deduction script, the redundancy check, and the consistency worker (for the search page).

Also, the database query wrappers in the Svelte application have been removed, since the db.prepare function by better-sqlite3 already supports generics, no additional error handling is required, and even additional features like .pluck() and .raw() are available. As a result, both the database application and the SvelteKit application now use the same pattern to access the database.

¹At the moment, the database application is simply a folder rather than a standalone package. A more systematic solution would be to turn the repository into a monorepo. I experimented with that a while ago, but it introduced enough complexity that I decided against it.