search: stemming (suffix stripping) + 18 tests

Deterministic English suffix stripping (stem), stemText/stemTokens, indexStemmed.
Worked around two haskell-on-sx string gotchas: take/drop over a String yield
char codes (rebuild via joinChars . map chr), and isSuffixOf's reverse trips ++
(manual suffix compare). 196/196.

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

lib/search/api.sx

@@ -6,7 +6,7 @@
 ;; rankTfIdf, rankBm25, topNTfIdf, topNBm25, fedIndex, aclFilter, searchTfIdfAcl,
 ;; topNTfIdfAcl, searchBm25Acl, prefixTerms, prefixDocs, prefixRankTfIdf,
 ;; paginate, pageTfIdf, pageBm25, resultCount, editDist, fuzzyTerms, fuzzyDocs,
-;; fuzzyRankTfIdf, highlight, snippet.
+;; fuzzyRankTfIdf, highlight, snippet, stem, stemText, stemTokens, indexStemmed.
 
 (define
   search/src
@@ -29,4 +29,6 @@
     "\n"
     search/fuzzy-src
     "\n"
-    search/highlight-src))
+    search/highlight-src
+    "\n"
+    search/stem-src))