[REFACTOR] Consolidate desktop UX/UI validation matrix and acceptance reporting

[ksamaschke]

Phase

REFACTOR

## Deliverable
Refine the validation matrix and acceptance-reporting structure after GREEN while preserving the desktop UX/UI gate.

## Dependencies
- Parent work item: #220.

## Completion evidence
- Cleanup notes for validation structure and acceptance reporting.

• Evidence that the validation gate remains intact.

  Acceptance criteria

  • Validation artifacts are easier to maintain.

• The cleanup does not weaken the desktop UX/UI acceptance gate.

  Parent: Work Item: Add screenshot-level validation and desktop acceptance checks #220