Repair authentication, migrations, tests, and delivery

[jon314159]

Summary

• fix access/refresh token validation and load the real database user for protected routes
• reject invalid and non-finite calculator inputs, including modulus-by-zero updates
• add an adoptable initial Alembic migration and safe SQLite test isolation
• split runtime/dev dependencies, remove vulnerable unused packages, and modernize Docker/CI publishing
• add regression coverage and a real browser registration/login/calculation flow

Verification

• 147 passed, 1 skipped; 92% coverage
• Alembic upgrade/downgrade/adoption and schema drift checks pass
• pip-audit: no known vulnerabilities
• docker compose config and Python bytecode compilation pass