search: result pagination (offset/limit) + 12 tests

paginate windows a ranked list (take lim . drop off); pageTfIdf/pageBm25 and
resultCount. 148/148.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/search/api.sx

@@ -4,7 +4,8 @@
 ;; interpreter. Public Haskell entry points: indexDoc, lookupTerm, deleteDoc,
 ;; docFreq, allTerms, tokens, positioned, evalQuery, parseQuery, searchQuery,
 ;; rankTfIdf, rankBm25, topNTfIdf, topNBm25, fedIndex, aclFilter, searchTfIdfAcl,
-;; topNTfIdfAcl, searchBm25Acl, prefixTerms, prefixDocs, prefixRankTfIdf.
+;; topNTfIdfAcl, searchBm25Acl, prefixTerms, prefixDocs, prefixRankTfIdf,
+;; paginate, pageTfIdf, pageBm25, resultCount.
 
 (define
   search/src
@@ -21,4 +22,6 @@
     "\n"
     search/fed-src
     "\n"
-    search/prefix-src))
+    search/prefix-src
+    "\n"
+    search/page-src))