feat(search): surface summary snippet when summary matched the query

Add a summary_snippet column to findEnrichmentData using ts_headline on
documents.summary, only when the summary's tsvector matches the query.
Expose it via SearchMatchData.summarySnippet / summaryOffsets and render
a "Zusammenfassung" / "Summary" / "Resumen" labelled row in the document
list — identical treatment to the transcription snippet row.

Fixes the case where a document appeared in search results with no
visible match explanation (e.g. searching "frucht" found a document
whose summary mentioned "Früchte").

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

frontend/src/lib/generated/api.ts

@@ -1588,9 +1588,9 @@ export interface components {
             totalPages?: number;
         };
         DocumentSearchResult: {
-            documents?: components["schemas"]["Document"][];
+            documents: components["schemas"]["Document"][];
             /** Format: int64 */
-            total?: number;
+            total: number;
             matchData: {
                 [key: string]: components["schemas"]["SearchMatchData"];
             };
@@ -1608,6 +1608,8 @@ export interface components {
             matchedReceiverIds: string[];
             matchedTagIds: string[];
             snippetOffsets: components["schemas"]["MatchOffset"][];
+            summarySnippet?: string;
+            summaryOffsets: components["schemas"]["MatchOffset"][];
         };
         IncompleteDocumentDTO: {
             /** Format: uuid */