ocaml: phase 5.1 min_jumps.ml baseline (greedy BFS-like min jumps = 4)

Greedy BFS-frontier style — track the farthest reach within the
current jump's reachable range, and bump the jump counter when i
runs into the current frontier:

  while !i < n - 1 do
    farthest := max(farthest, i + arr.(i));
    if !i = !cur_end then begin
      jumps := !jumps + 1;
      cur_end := !farthest
    end;
    i := !i + 1
  done

For [2; 3; 1; 1; 2; 4; 2; 0; 1; 1] (n = 10), the optimal jump
sequence 0 -> 1 -> 4 -> 5 -> 9 uses 4 jumps.

Tests greedy-with-frontier pattern, three parallel refs
(jumps, cur_end, farthest), mixed for-style index loop using ref.

201 baseline programs total.

plans/ocaml-on-sx.md

@@ -407,6 +407,14 @@ _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.
+- 2026-05-11 Phase 5.1 — min_jumps.ml baseline (greedy BFS-like
+  min jumps to reach end of [2;3;1;1;2;4;2;0;1;1] = 4). At each
+  position track the farthest reach within the current "BFS
+  layer"; when i reaches the layer end, bump jumps and extend to
+  farthest. Optimal jump sequence 0→1→4→5→9 = 4 jumps. Tests
+  greedy-with-frontier idiom, three parallel refs (jumps, cur_end,
+  farthest), mixed for-style index loop using ref. 201 baseline
+  programs total.
 - 2026-05-11 Phase 5.1 — combinations.ml baseline (C(9, 4) = 126
   enumerated). Pascal-style recursive split: with first element h,
   combinations either include h (recurse with k−1 on rest) or