Migration 003 created tables with INTEGER keys referencing TEXT primary
keys from migration 002, causing 'no such column' errors. Fix by
properly dropping old tables before recreating with the integer schema.
Rewrite all tests to use the queries.go API (which matches the live
schema) instead of the model-based API (which expected the old UUID
schema).
CreateUser, GetUserByNick, GetUserByToken exist in both db.go (model-based,
used by tests) and queries.go (simple, used by handlers). Rename the
model-based variants to CreateUserModel, GetUserByNickModel, and
GetUserByTokenModel to resolve the compilation error.