feat(phase2): llm report writer (P5.3)

- New module src/pf1e_simulator/report.py with ReportContext, build_report_context,
  LLMReportPolicy, ReportBudget, format_llm_report, build_report_prompt
- Prompt pack fixture: tests/fixtures/prompt_pack_fs/report.md (FR narrator)
- CLI integration: --llm-report + --output flags, mutually exclusive with --transcript
- Budget enforcement: ReportBudget integrates with CostBudget, allows max_retries+1 calls
- Tests: test_report_context, test_report_prompt_pack, test_llm_report_policy,
  test_format_llm_report, test_cli_llm_report, test_report_budget (27 new tests)

tests/test_report_prompt_pack.py

@@ -0,0 +1,67 @@
+"""Tests for report prompt pack (P5.3 T2)."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from pf1e_simulator.prompt import PromptPack
+from pf1e_simulator.report import build_report_context, build_report_prompt
+from pf1e_simulator.runner import CombatantAttrition, EncounterReport
+
+
+def test_report_prompt_pack_version_stable() -> None:
+    """Prompt pack version hash is stable for the fixture."""
+    pack_dir = Path(__file__).resolve().parent / "fixtures" / "prompt_pack_fs"
+    pack = PromptPack.load(pack_dir)
+
+    report_version = pack.prompt_version("report")
+    assert report_version.startswith("0.1.0-test:report:")
+    assert len(report_version.split(":")[2]) == 12  # hash12
+
+
+def test_report_prompt_renders() -> None:
+    """build_report_prompt renders the context correctly."""
+    pack_dir = Path(__file__).resolve().parent / "fixtures" / "prompt_pack_fs"
+    pack = PromptPack.load(pack_dir)
+    template = pack.get("report")
+
+    encounter = EncounterReport(
+        runs=100,
+        seed=1,
+        wins={"players": 65, "monsters": 33},
+        draws=2,
+        avg_rounds=7.2,
+        attrition={
+            "goblin": CombatantAttrition(2.45, 0.12, 18.30, 4.20, 0.00),
+            "orc": CombatantAttrition(3.20, 0.25, 28.40, 15.60, 0.00),
+        },
+    )
+
+    ctx = build_report_context(
+        encounter=encounter,
+        spec_name="test",
+    )
+
+    prompt = build_report_prompt(ctx, template)
+
+    # Should contain the system prompt text
+    assert "Vous êtes le narrateur" in prompt
+    assert "Bilan d'équilibrage" in prompt
+    assert "Danger et attrition" in prompt
+    # Should contain the rendered encounter data
+    assert "Victoires players : 65.0%" in prompt or "Victoires players : 65" in prompt
+    assert "goblin" in prompt
+    assert "orc" in prompt
+    # Should contain attrition
+    assert "Attrition moyenne par combatant" in prompt
+    assert "touches" in prompt
+
+
+def test_report_prompt_version_different_from_nl_default() -> None:
+    """report prompt_version differs from nl_default."""
+    pack_dir = Path(__file__).resolve().parent / "fixtures" / "prompt_pack_fs"
+    pack = PromptPack.load(pack_dir)
+
+    report_version = pack.prompt_version("report")
+    nl_version = pack.prompt_version("nl_default")
+    assert report_version != nl_version