feat(frontend): replace all name concatenation with displayName

- Add displayName default method to PersonSummaryDTO
- Update native SQL queries to include title, person_type columns
- Add getInitials() utility to personFormat.ts
- Update abbreviateName/abbreviateCompact for nullable firstName
- Replace firstName+lastName concatenation with displayName in all
  person-displaying components and server load files
- Regenerate API types with displayName on Person and PersonSummaryDTO

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

backend/src/test/java/org/raddatz/familienarchiv/controller/PersonControllerTest.java

@@ -73,8 +73,10 @@ class PersonControllerTest {
     private PersonSummaryDTO mockPersonSummary(String firstName, String lastName) {
         return new PersonSummaryDTO() {
             public java.util.UUID getId() { return UUID.randomUUID(); }
+            public String getTitle() { return null; }
             public String getFirstName() { return firstName; }
             public String getLastName() { return lastName; }
+            public String getPersonType() { return "PERSON"; }
             public String getAlias() { return null; }
             public Integer getBirthYear() { return null; }
             public Integer getDeathYear() { return null; }