test(person): controller returns 409 PERSON_RENAME_CONFLICT on optimistic-lock

Add updatePerson_returns409_whenRenameConflict to PersonControllerTest: exercises
the full controller→exception-handler path, not just the service layer. Verifies
HTTP 409 + $.code = PERSON_RENAME_CONFLICT when updatePerson throws a conflict.

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

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

@@ -333,6 +333,21 @@ class PersonControllerTest {
                 .andExpect(jsonPath("$.lastName").value("Müller"));
     }
 
+    @Test
+    @WithMockUser(authorities = "WRITE_ALL")
+    void updatePerson_returns409_whenRenameConflict() throws Exception {
+        UUID id = UUID.randomUUID();
+        when(personService.updatePerson(eq(id), any()))
+                .thenThrow(DomainException.conflict(ErrorCode.PERSON_RENAME_CONFLICT,
+                        "Concurrent block edit during rename"));
+
+        mockMvc.perform(put("/api/persons/{id}", id)
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"firstName\":\"Augusta\",\"lastName\":\"Raddatz\",\"personType\":\"PERSON\"}"))
+                .andExpect(status().isConflict())
+                .andExpect(jsonPath("$.code").value("PERSON_RENAME_CONFLICT"));
+    }
+
     // ─── POST /api/persons/{id}/merge ─────────────────────────────────────────
 
     @Test