Add PHPUnit coverage: Entity CRUD, Area placing, Sessions, Utils ...

- EntityCrudTest: 6 tests covering update, get, remove, id, to_array
- AreaPlacingTest: 2 tests for place_in_area and place_in_area_id
- SessionsTest: 4 tests for create, get_by_token, close, status
- UtilsTest: 7 tests for response_error/success, table_row_is_exists,
  generate_token, dayname_translate, fast_ping_tcp
- TestApp helper + bootstrap init with SQLite :memory: for app() dependencies
- Update server-audit.md: 36 total tests, expand coverage roadmap