feat(search): add TagService.findByNameContaining for NL tag resolution

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

backend/src/main/java/org/raddatz/familienarchiv/tag/TagService.java

@@ -46,6 +46,10 @@ public class TagService {
         return enrichWithRelatives(matched);
     }
 
+    public List<Tag> findByNameContaining(String fragment) {
+        return tagRepository.findByNameContainingIgnoreCase(fragment);
+    }
+
     public Tag getById(UUID id) {
         return tagRepository.findById(id)
                 .orElseThrow(() -> DomainException.notFound(ErrorCode.TAG_NOT_FOUND, "Tag not found: " + id));

backend/src/test/java/org/raddatz/familienarchiv/tag/TagServiceTest.java

@@ -666,4 +666,17 @@ class TagServiceTest {
         // verify findAllById was called at least twice: once for extras, once inside resolveEffectiveColors
         verify(tagRepository, atLeastOnce()).findAllById(any());
     }
+
+    // ─── findByNameContaining ─────────────────────────────────────────────────
+
+    @Test
+    void findByNameContaining_delegatesToRepository() {
+        Tag krieg = Tag.builder().id(UUID.randomUUID()).name("Krieg").build();
+        when(tagRepository.findByNameContainingIgnoreCase("krieg")).thenReturn(List.of(krieg));
+
+        List<Tag> result = tagService.findByNameContaining("krieg");
+
+        assertThat(result).containsExactly(krieg);
+        verify(tagRepository).findByNameContainingIgnoreCase("krieg");
+    }
 }