test: add 149 unit tests across core, auth, config, message crates
Test coverage increased from ~34 to 183 tests (zero failures):
- erp-core (21): version check, pagination, API response, error mapping
- erp-auth (39): org tree building, DTO validation, error conversion,
password hashing, user model mapping
- erp-config (57): DTO validation, numbering reset logic, menu tree
building, error conversion. Fixed BatchSaveMenusReq nested validation
- erp-message (50): DTO validation, template rendering, query defaults,
error conversion
- erp-workflow (16): unchanged (parser + expression tests)
All tests are pure unit tests requiring no database.
ee65b6e3c9