feat(runner): Monte Carlo runner, closed-form metrics and balance CLI

Adds the S6 layer on top of the deterministic combat engine:
- metrics.py: closed-form binomial statistics (win rate, standard error,
  3-sigma confidence band) with clamped degenerate proportions.
- runner.py: EncounterSpec/Side definitions, per-run SeededRng streams,
  global duplicate-id disambiguation, attrition averages per combatant.
- cli.py: pf1e-sim entry point producing a French balance report with
  win rates, 3-sigma bands, draws, rounds, and attrition.
- Movement fix: greedy straight-line heuristic could oscillate at walls;
  _step_toward now follows the true shortest path via an unbounded
  Dijkstra cost field from the target (Grid.reachable budget=None).
- Regression tests: melee unit routes around a wall and engages; grid
  unbounded-budget coverage.

tests/test_cli.py

@@ -0,0 +1,59 @@
+"""Tests for the pf1e-sim command-line interface."""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    import pytest
+
+from pf1e_simulator.cli import main
+
+ROOT = Path(__file__).resolve().parents[1]
+MAP = ROOT / "data" / "maps" / "sample_arena.yaml"
+GOBLIN = ROOT / "data" / "monsters" / "goblin.json"
+ORC = ROOT / "data" / "monsters" / "orc.json"
+
+
+def test_cli_prints_balance_report(capsys: pytest.CaptureFixture[str]) -> None:
+    rc = main(
+        [
+            "--map",
+            str(MAP),
+            "--side",
+            "players",
+            str(GOBLIN),
+            str(GOBLIN),
+            str(GOBLIN),
+            "--side",
+            "monsters",
+            str(ORC),
+            str(ORC),
+            "--runs",
+            "50",
+            "--seed",
+            "1",
+        ]
+    )
+    out = capsys.readouterr().out
+    assert rc == 0
+    assert "Rapport d'équilibrage" in out
+    assert "Victoires players" in out
+    assert "Victoires monsters" in out
+    assert "bande 3σ" in out
+    assert "Nuls" in out
+    assert "Rounds moyens" in out
+    assert "Attrition moyenne" in out
+
+
+def test_cli_rejects_side_not_in_deployment(capsys: pytest.CaptureFixture[str]) -> None:
+    rc = main(["--map", str(MAP), "--side", "bogus", str(GOBLIN), "--runs", "10"])
+    assert rc == 2
+    assert "deployment" in capsys.readouterr().err
+
+
+def test_cli_rejects_missing_deployment_side(capsys: pytest.CaptureFixture[str]) -> None:
+    rc = main(["--map", str(MAP), "--side", "players", str(GOBLIN), "--runs", "10"])
+    assert rc == 2
+    assert "monsters" in capsys.readouterr().err