UFAL/User registration duplicites fix

[Paurikova2]

Problem description

After the import and during DSpace usage, multiple user registrations were created for a single EPerson.

Problem: If an EPerson already existed and was not newly created during the process, a new user registration was still created.

Manual Testing (if applicable)

• Added to testing scenarios

Copilot review

• Requested review from Copilot

[Copilot]

Pull request overview

This PR addresses duplicate user_registration rows being created for the same EPerson during import/usage in CLARIN-DSpace (DSpace 7 REST backend), by enforcing uniqueness at both the application and database layers and adding integration tests to validate the behavior.

Changes:

• Prevent duplicate registrations by updating an existing registration when eperson_id matches (service-layer guard).
• Ensure the EPerson import endpoint does not leave behind an automatically created “Unknown” registration.
• Add DB migrations introducing a unique index on user_registration.eperson_id and expand DAO email lookup to support semicolon-separated email values.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
dspace-api/src/main/java/org/dspace/content/clarin/ClarinUserRegistrationServiceImpl.java	Updates create() to update an existing registration when eperson_id already exists.
dspace-api/src/main/java/org/dspace/content/dao/impl/clarin/ClarinUserRegistrationDAOImpl.java	Expands findByEmail matching to handle semicolon-separated email strings.
dspace-server-webapp/src/main/java/org/dspace/app/rest/repository/ClarinEPersonImportController.java	Removes auto-created registrations during EPerson import so registrations are managed by the dedicated endpoint.
dspace-api/src/main/resources/.../postgres/V7.6_2026.03.10__user_registration_unique_eperson_id.sql	Adds a (partial) unique index on eperson_id in PostgreSQL.
dspace-api/src/main/resources/.../h2/V7.6_2026.03.10__user_registration_unique_eperson_id.sql	Adds a unique index on eperson_id in H2 for tests/dev.
dspace-server-webapp/src/test/java/org/dspace/app/rest/ClarinUserRegistrationServiceImplIT.java	Adds integration tests covering dedup/update behavior and null-eperson cases.
dspace-server-webapp/src/test/java/org/dspace/app/rest/ClarinEPersonImportControllerIT.java	Adds an integration test asserting EPerson import does not create a user registration.