Add CreateTestDatabase function for parallel isolated test databases per package.
- Add CreateTestDatabase() for isolated test DBs (parallel-safe)
- Move all TestMain functions to per-package testmain_test.go files
- Remove old TestMain from handlers_test.go, jwt_test.go, main_test.go
- Add JWT init guard in main.go to skip when -test.* flags detected
- Update testdb.go with admin DSN and proper cleanup
- Rename test database to crussell_test_db for consistency
- Replace testdb.NewPool + testdb.Migrate pattern with CreateTestDatabase
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
