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.

plans/ocaml-on-sx.md

@@ -407,6 +407,9 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-08 Phase 5.1 — anagrams.ml baseline (18/18 pass). Counts
+  anagram-equivalence groups via Hashtbl + List.sort + String.get +
+  for-loop. `["eat";"tea";"tan";"ate";"nat";"bat"]` → 3 groups.
 - 2026-05-08 Phase 5.1 — lambda_calc.ml baseline (17/17 pass). Untyped
   lambda calculus interpreter using two ADTs (`type term = Var | Abs |
   App | Num`, `type value = VNum | VClos`), an env as `(string * value)