fix(search): use to_tsquery('simple') for prefix transform to avoid German stop word collision

Words like "Wille" stem to "will" via the German Snowball stemmer, which is
also a German stop word. The prefix-transform step (websearch_to_tsquery text →
regexp_replace → to_tsquery) was passing already-stemmed lexemes back through
the German dictionary, causing them to be silently dropped as stop words. Using
the 'simple' configuration skips stop-word processing entirely while the
tsvector @@ tsquery comparison still works because lexemes are matched by
string value, not by configuration.

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

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

@@ -87,7 +87,7 @@ public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSp
             SELECT d.id FROM documents d
             CROSS JOIN LATERAL (
                 SELECT CASE WHEN websearch_to_tsquery('german', :query)::text <> ''
-                            THEN to_tsquery('german', regexp_replace(
+                            THEN to_tsquery('simple', regexp_replace(
                                      websearch_to_tsquery('german', :query)::text,
                                      '''([^'']+)''',
                                      '''\\1'':*',
@@ -149,7 +149,7 @@ public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSp
             FROM documents d
             CROSS JOIN LATERAL (
                 SELECT CASE WHEN websearch_to_tsquery('german', :query)::text <> ''
-                            THEN to_tsquery('german', regexp_replace(
+                            THEN to_tsquery('simple', regexp_replace(
                                      websearch_to_tsquery('german', :query)::text,
                                      '''([^'']+)''',
                                      '''\\1'':*',

backend/src/test/java/org/raddatz/familienarchiv/repository/DocumentFtsTest.java

@@ -179,6 +179,22 @@ class DocumentFtsTest {
         assertThat(ids).isEmpty();
     }
 
+    @Test
+    void should_find_document_whose_transcription_contains_word_that_stems_to_german_stop_word() {
+        // "Wille" stems to "will" via the German Snowball stemmer.
+        // "will" is also a German stop word, so to_tsquery('german','will:*') drops it.
+        // The prefix-transform step must use to_tsquery('simple',...) to avoid this.
+        Document doc = documentRepository.saveAndFlush(document("Foto"));
+        UUID annotationId = annotation(doc.getId());
+        blockRepository.saveAndFlush(block(doc.getId(), annotationId, "Der Wille des Volkes", 0));
+        em.flush();
+        em.clear();
+
+        List<UUID> ids = documentRepository.findRankedIdsByFts("Wille");
+
+        assertThat(ids).contains(doc.getId());
+    }
+
     @Test
     void should_not_throw_when_query_contains_invalid_tsquery_syntax() {
         documentRepository.saveAndFlush(document("Brief"));