Implements IMemberService with Create/Read/Update/soft-Delete operations,
NickName/zh-name search, status and hasUser filtering, and full xUnit coverage
(11 tests). Uses separate user-lookup query for InMemory DB compatibility; detaches
entity after soft-delete so query-filter assertions work correctly in tests.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Chris Chen