sql/sqlite.ts: Make FK constraints do something

They don't by default, because they didn't in older versions of
SQLite and some older applications might rely on that. You have to
send an explicit pragma prior to opening a transaction to make them
take effect.

src/sql/sqlite.ts

@@ -92,6 +92,7 @@ class SqliteDataSource implements DataSource {
     const db = new Database(this._path);
 
     db.defaultSafeIntegers();
+    db.prepare("pragma foreign_keys = on").run();
     db.prepare("begin").run();
 
     try {