[Task]: Testing — Registration acceptance tests

﻿## Parent user story
#6

## Technical objective
Cover Given/When/Then cases for happy path and duplicate email.

## Implementation notes
Prefer API tests first; add UI smoke if time allows.

## Expected result
Failing tests exist before merge if AC broken.

## Testing requirements
Automated tests in CI or local test project.

## Estimated effort
M (half day)

## Team
Testing
