feat(search): partial-word matching via to_tsquery prefix queries

Replace websearch_to_tsquery with a CROSS JOIN LATERAL subquery that
appends :* to each lexeme so prefix matches work (e.g. "furchtb" finds
"furchtbar"). websearch_to_tsquery still handles the safe tokenisation
of user input (stop words, special chars, operators); regexp_replace
then adds :* before to_tsquery re-parses the result.

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

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

@@ -83,8 +83,17 @@ public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSp
 
     @Query(nativeQuery = true, value = """
             SELECT d.id FROM documents d
-            WHERE d.search_vector @@ websearch_to_tsquery('german', :query)
+            CROSS JOIN LATERAL (
-            ORDER BY ts_rank(d.search_vector, websearch_to_tsquery('german', :query)) DESC,
+                SELECT CASE WHEN websearch_to_tsquery('german', :query)::text <> ''
+                            THEN to_tsquery('german', regexp_replace(
+                                     websearch_to_tsquery('german', :query)::text,
+                                     '''([^'']+)''',
+                                     '''\\1'':*',
+                                     'g'))
+                       END AS pq
+            ) q
+            WHERE d.search_vector @@ q.pq
+            ORDER BY ts_rank(d.search_vector, q.pq) DESC,
                      d.meta_date DESC NULLS LAST
             """)
     List<UUID> findRankedIdsByFts(@Param("query") String query);
@@ -99,44 +108,59 @@ public interface DocumentRepository extends JpaRepository<Document, UUID>, JpaSp
      *   <li>Boolean — whether the sender's name matched the query</li>
      *   <li>String — comma-separated matched receiver UUIDs, or null</li>
      *   <li>String — comma-separated matched tag UUIDs, or null</li>
+     *   <li>String — summary snippet with \x01/\x02 delimiters, or null if summary didn't match</li>
      * </ol>
      * Short-circuit before calling this method when {@code ids} is empty or {@code query} is blank.
      */
     @Query(nativeQuery = true, value = """
             SELECT
                 d.id,
-                ts_headline('german', d.title, websearch_to_tsquery('german', :query),
+                ts_headline('german', d.title, q.pq,
                     'StartSel=' || chr(1) || ',StopSel=' || chr(2) || ',HighlightAll=true')
                     AS title_headline,
                 CASE WHEN best_block.text IS NOT NULL THEN
-                    ts_headline('german', best_block.text, websearch_to_tsquery('german', :query),
+                    ts_headline('german', best_block.text, q.pq,
                         'StartSel=' || chr(1) || ',StopSel=' || chr(2) || ',MaxWords=50,MinWords=20')
                 END AS transcription_snippet,
                 (s.id IS NOT NULL AND
                  to_tsvector('german', COALESCE(s.first_name, '') || ' ' || COALESCE(s.last_name, ''))
-                     @@ websearch_to_tsquery('german', :query))
+                     @@ q.pq)
                     AS sender_matched,
                 (SELECT string_agg(r.id::text, ',')
                  FROM document_receivers dr
                  JOIN persons r ON r.id = dr.person_id
                  WHERE dr.document_id = d.id
                    AND to_tsvector('german', COALESCE(r.first_name, '') || ' ' || r.last_name)
-                           @@ websearch_to_tsquery('german', :query)
+                           @@ q.pq
                 ) AS matched_receiver_ids,
                 (SELECT string_agg(t.id::text, ',')
                  FROM document_tags dt
                  JOIN tag t ON t.id = dt.tag_id
                  WHERE dt.document_id = d.id
-                   AND to_tsvector('german', t.name) @@ websearch_to_tsquery('german', :query)
+                   AND to_tsvector('german', t.name) @@ q.pq
-                ) AS matched_tag_ids
+                ) AS matched_tag_ids,
+                CASE WHEN d.summary IS NOT NULL AND d.summary <> ''
+                          AND to_tsvector('german', d.summary) @@ q.pq
+                     THEN ts_headline('german', d.summary, q.pq,
+                              'StartSel=' || chr(1) || ',StopSel=' || chr(2) || ',MaxWords=50,MinWords=20')
+                END AS summary_snippet
             FROM documents d
+            CROSS JOIN LATERAL (
+                SELECT CASE WHEN websearch_to_tsquery('german', :query)::text <> ''
+                            THEN to_tsquery('german', regexp_replace(
+                                     websearch_to_tsquery('german', :query)::text,
+                                     '''([^'']+)''',
+                                     '''\\1'':*',
+                                     'g'))
+                       END AS pq
+            ) q
             LEFT JOIN persons s ON s.id = d.sender_id
             LEFT JOIN LATERAL (
                 SELECT tb.text
                 FROM transcription_blocks tb
                 WHERE tb.document_id = d.id
-                  AND to_tsvector('german', tb.text) @@ websearch_to_tsquery('german', :query)
+                  AND to_tsvector('german', tb.text) @@ q.pq
-                ORDER BY ts_rank(to_tsvector('german', tb.text), websearch_to_tsquery('german', :query)) DESC
+                ORDER BY ts_rank(to_tsvector('german', tb.text), q.pq) DESC
                 LIMIT 1
             ) best_block ON true
             WHERE d.id IN :ids

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

@@ -79,6 +79,16 @@ class DocumentFtsTest {
         assertThat(ids).hasSize(1);
     }
 
+    @Test
+    void should_find_document_by_partial_word_prefix() {
+        documentRepository.saveAndFlush(document("Ein furchtbarer Brief"));
+        em.clear();
+
+        List<UUID> ids = documentRepository.findRankedIdsByFts("furchtb");
+
+        assertThat(ids).hasSize(1);
+    }
+
     @Test
     void should_not_find_document_when_term_absent() {
         documentRepository.saveAndFlush(document("Familienfoto"));