feat: add findByAliasIgnoreCase to PersonRepository

Required by MassImportService to look up persons by their full name
stored as alias before deciding to create a new Person record.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/main/java/org/raddatz/familienarchiv/repository/PersonRepository.java

@@ -1,6 +1,7 @@
 package org.raddatz.familienarchiv.repository;
 
 import java.util.List;
+import java.util.Optional;
 import java.util.UUID;
 
 import org.raddatz.familienarchiv.model.Person;
@@ -22,4 +23,7 @@ public interface PersonRepository extends JpaRepository<Person, UUID> {
 
     // Hilfsmethode: Alle sortiert laden (für den leeren Status)
     List<Person> findAllByOrderByLastNameAscFirstNameAsc();
+
+    // Lookup by full alias string, used during ODS mass import
+    Optional<Person> findByAliasIgnoreCase(String alias);
 }