ocaml: phase 5.1 bipartite.ml baseline (7-node bipartite, 4 in color 0)

BFS-based 2-coloring of an undirected graph:

  edges (undirected):
    0-1  0-3  1-2  1-4  2-5  3-4  3-6  5-6

  Partition: {0, 2, 4, 6} vs {1, 3, 5} (no odd cycles)

Returns count of color-0 vertices (4) on success, -1 on odd-cycle
detection.

Tests Queue-based BFS with a source-loop wrapper for disconnected
graphs, `1 - color.(u)` toggle, color-equality conflict check
on already-colored neighbors.

164 baseline programs total.

lib/ocaml/baseline/expected.json

@@ -12,6 +12,7 @@
   "bisect.ml": 141,
   "bigint_add.ml": 28,
   "binary_heap.ml": 123456789,
+  "bipartite.ml": 4,
   "bits.ml": 21,
   "balance.ml": 3,
   "base_n.ml": 17,