Admin Vouchers API — Changes

Two updates to the admin vouchers list endpoint (GET /admin/v1/vouchers).

1. Redeemed-by user info

Each voucher in the response now includes a redeemedBy object identifying the user who redeemed it, resolved from the auth database:

{
  "voucherId": "...",
  "code": "ABCD-1234",
  "status": "Redeemed",
  "redeemedByUserId": "auth0|123",
  "redeemedBy": {
    "id": "auth0|123",
    "fullName": "Filan Fisteku",
    "email": "[email protected]"
  },
  "redeemedAt": "2026-07-01T10:15:00Z"
}

redeemedBy is null for vouchers that haven't been redeemed.
The existing redeemedByUserId field is unchanged, so nothing breaks for current consumers.
Users are batch-loaded per page (one query for all distinct user IDs), following the same pattern as the admin pay-to-view purchases endpoint.

Files changed

File	Change
`core/PicTv.Application/Dtos/Vouchers/VoucherDto.cs`	Added `RedeemedBy` property and new `VoucherRedeemedByDto` (`Id`, `FullName`, `Email`)
`core/PicTv.Application/Vouchers/Queries/GetAdminVouchers/GetAdminVouchersQueryHandler.cs`	Injected `IAuthDbContext`; added `PopulateRedeemedByAsync` to enrich results with user name and email

2. Order by reason

New optional query parameter orderByReason (boolean, default false):

GET /admin/v1/vouchers?page=1&orderByReason=true

When true, vouchers are sorted alphabetically by reason, with newest-first (createdAt descending) as the tiebreaker.
When omitted or false, the existing default ordering (newest first by createdAt) applies.

Files changed

File	Change
`api/PicTv.Api/Routes/VoucherRoutes.cs`	Added `orderByReason` query parameter to the admin list endpoint
`core/PicTv.Application/Vouchers/Queries/GetAdminVouchers/GetAdminVouchersQuery.cs`	Added `OrderByReason` property (defaults to `false`)
`core/PicTv.Application/Vouchers/Queries/GetAdminVouchers/GetAdminVouchersQueryHandler.cs`	Applies `OrderBy(Reason).ThenByDescending(CreatedAt)` when the flag is set

Notes

No database or migration changes — RedeemedByUserId, RedeemedAt, and Reason were already stored on the Voucher entity.
If more sort columns are needed later (status, redeemed date, …), the boolean flag should be replaced with an orderBy enum parameter.