Wrap /admin/errors/competitions-without-plays response in DTO

[Copilot]

Endpoint returns naked collection instead of wrapped response object per API standardization effort.

Changes

• New DTO: CompetitionsWithoutPlaysResponse with Items property wrapping List<CompetitionWithoutPlaysDto>
• Service layer: Updated IAdminService.GetCompetitionsWithoutPlays() return type from Result<List<T>> to Result<CompetitionsWithoutPlaysResponse>
• Controller: Changed endpoint return type to ActionResult<CompetitionsWithoutPlaysResponse>

Response Format

Before:

[
  { "contestId": "...", "playCount": 0, ... }
]

After:

{
  "items": [
    { "contestId": "...", "playCount": 0, ... }
  ]
}

Frontend already handles both formats via optional chaining: res.data?.items ?? res.data

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Wrap /admin/errors/competitions-without-plays response</issue_title>
<issue_description>Location: AdminController.cs:125

Current: Returns naked collection
Target: Return wrapped response object

Acceptance Criteria:

• Create response DTO
• Update controller
• Update frontend if needed
• Update tests
• Verify Swagger

See docs/API-WRAPPER-REFACTORING.md</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Wrap /admin/errors/competitions-without-plays response #9

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