Status filter (pending/success/failed) works alongside the existing
staff/date filters, all sharing one buildTransactionFilter() helper so
listing and export never drift apart.

Export is a new GET /admin/transactions/export route: same filters,
no pagination limit (exports everything matching, not just the current
page), CSV with a UTF-8 BOM so Excel on Windows renders Vietnamese
diacritics correctly instead of mangling them.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017KPzWwuTEeX2vXGXvyGn4q