feat(06.2-04): frontend — user_handle filter, fetch+Blob export, daily-export section
- adminListAuditLog: rename user_id param to user_handle (backend API change)
- adminExportAuditLogCsv(): fetch+Blob pattern — sends Bearer header (D-13, T-06.2-04-03)
- adminListDailyExports(): raw fetch returning JSON for daily export listing (D-17)
- adminDownloadDailyExport(date): fetch+Blob download with audit-{date}.csv filename (D-17)
- AuditLogTab: rename filters.user_id to filters.user_handle + label 'User handle' (D-12, C-5)
- AuditLogTab: exportCsv() replaced with async fetch+Blob call, exportingCsv loading state
- AuditLogTab: daily exports section below pagination — date dropdown + Download button (D-17, C-4)
- window.location.href removed from AuditLogTab (broken auth bypass closed)
- Build exits 0, full backend suite: 337 passed, 1 pre-existing failure
curo1305
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