SQL Server treats `;` as a statement terminator, not a batch separator.
The previous logic split multi-statement SQL by `;` and executed each
independently, breaking variable/CTE scope across statements.
Send the entire SQL as a single batch via `simple_query` so DECLARE,
SET, and CTE definitions remain visible to subsequent statements.
Split only on the `GO` client directive when present.
Refactor all database drivers, query execution, schema operations, and
business logic into a shared `dbx-core` crate. The Tauri desktop app
becomes a thin shell delegating to dbx-core, enabling future web and
CLI frontends to reuse the same core.
t8y2