test(documents): wire content-index mocks into the list route test

P2-1. The list GET now issues a documentContentIndex lookup and unions a
content-token OR branch when a search term is present, so the existing route
test gains the mock + the third OR branch in its where assertion. Fix the
backfill test's findFirst mock signature under strict tsc.

src/components/documents/__tests__/document-card.test.tsx

@@ -68,7 +68,7 @@ describe("<DocumentCard>", () => {
       <DocumentCard
         document={doc({
           servingClass: "attachment",
-    hasContentIndex: false,
+          hasContentIndex: false,
           mimeType: "application/octet-stream",
           filename: "befund.docx",
           title: null,