ocaml: phase 5.1 anagrams.ml baseline (18/18 pass)

Group anagrams by canonical (sorted-chars) key using Hashtbl +
List.sort. Demonstrates char-by-char traversal via String.get + for-loop +
ref accumulator + Hashtbl as a multi-valued counter.

lib/ocaml/baseline/expected.json

@@ -1,4 +1,5 @@
 {
+  "anagrams.ml": 3,
   "btree.ml": 39,
   "calc.ml": 13,
   "closures.ml": 315,