Replace raw db.execute tuple casts with queryRows/rowsFrom/execResult/
affectedRows helpers from lib/db, drop redundant mysql2 casts on typed
query builders, and centralize per-test fakeForm into test/fake-form.
Update db mocks in tests so helpers resolve against mocked execute.
checkLogin now verifies and migrates all known password formats without
configuration: bcrypt, argon2id/argon2i/argon2d, unsalted md5/sha1/sha256/
sha512, double-md5 (UberCMS/Butterfly), salted md5 with embedded salt
(hash:salt, salt:hash, hash$salt), and a guarded plaintext fallback.
Every successful legacy login rewrites the stored hash to bcrypt, so the
CONVERT_PASSWORDS flag is no longer required (kept for deploy compatibility).
The username normalization, dummy-hash constant, password check and
email-verification gate were duplicated between precheckLogin and the
NextAuth credentials authorize handler. Move them into a single
login-core module so both paths share one source of truth and stay
consistent.