v1.4.2: Docs honesty + test marker

Type: PATCH (no API or behavior changes)

Fixes:

• Docs honesty in range_aggregator.py: The hero_player parameter docstring and the module-level docstring both described P0 as making the "first postflop decision," which is backwards. In HUNL, slot 0 is the SB seat (button) — first to act PREFLOP, last to act POSTFLOP. Slot 1 is the BB seat — last to act PREFLOP, first to act POSTFLOP. Both docstrings now state the position semantics correctly and include a note on the BB-defending workflow (hero_player=1 AND hero_range=bb_range so BB cards land in the BB seat).

• Slow-test marker: tests/test_river_parity_vs_brown.py::test_river_parity_vs_brown now carries @pytest.mark.slow so it is excluded from the default CI suite (which runs -m 'not slow') and only executes when developers explicitly opt in. Formalizes the opt-in posture that was already implicit in CI config.

Honest framing:

No API or behavior changes. Docs say what the code has always done; the slow-test marker formalizes existing opt-in posture. Safe drop-in upgrade from v1.4.1.

Smoke tests: 31/31 passed (test_dcfr_diff, test_exploit_diff, test_range_vs_range_aggregator).