Stand up the Engine/PIP surface for MAT-WP-0001

Declare layer.yaml, add a Python engine over a local SQLite store,
and cover deterministic assessment, the §13 gap register, stance-map
inventory, claim guardrails, and the gate-house review path with tests.

Assistant: grok
Assistant-Session: 01a04ceb-150e-7e80-a542-ec8b1372e164

tests/conftest.py

@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from pathlib import Path
+
+import pytest
+
+from maturity_engine.engine import Engine
+from maturity_engine.models import Evidence
+
+INSTANT = datetime(2026, 8, 29, 12, 0, tzinfo=timezone.utc)
+
+
+@pytest.fixture
+def engine(tmp_path: Path) -> Engine:
+    inst = Engine.open(tmp_path / "maturity.sqlite")
+    inst.bootstrap(at=INSTANT)
+    yield inst
+    inst.close()
+
+
+def evidence(
+    engine: Engine,
+    subject: str,
+    kind: str,
+    *,
+    at: datetime = INSTANT,
+    until: datetime | None = None,
+    by: str = "fixture",
+) -> Evidence:
+    return Evidence(
+        id=engine.evidence_id(subject, kind, at),
+        subject=subject,
+        kind=kind,
+        submitted_by=by,
+        submitted_at=at,
+        valid_from=at,
+        valid_until=until,
+        payload={"kind": kind},
+    )