fix: classify Steuerfinanzamt and Reichsfechtschule as institutions

Add "amt" and "schule" suffixes to INSTITUTION_END in PersonTypeClassifier
so German government offices and schools are auto-classified on import.

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

backend/src/test/java/org/raddatz/familienarchiv/service/PersonTypeClassifierTest.java

@@ -28,7 +28,9 @@ class PersonTypeClassifierTest {
             "'Arthur Collignon GmbH', INSTITUTION",
             "'Firma Auschrath', INSTITUTION",
             "'Westermann u Co', INSTITUTION",
-            "'Architekt Korschelt u Renker', INSTITUTION"
+            "'Architekt Korschelt u Renker', INSTITUTION",
+            "'Steuerfinanzamt', INSTITUTION",
+            "'Reichsfechtschule', INSTITUTION"
     })
     void classify_institutionEntries(String input, PersonType expected) {
         assertThat(PersonTypeClassifier.classify(input)).isEqualTo(expected);