feat(gateway): C8 PM-decision gate windowed satisfaction

_check_pm_decision_required now requires the latest journal:decision
within pm_decision_window_seconds (default 300). Older decisions no
longer satisfy the gate. Adds JournalService.latest_decision_at.

Future-tighten (out of scope): per-verb-group consumption tracking
would need persistent state — Choreographer is per-request today.

tests/unit/gateway/test_resume.py

@@ -14,6 +14,7 @@ that gap. These tests pin the four behaviors:
 
 from __future__ import annotations
 
+from datetime import UTC, datetime
 from typing import Any
 from unittest.mock import AsyncMock, MagicMock
 from uuid import uuid4
@@ -44,6 +45,13 @@ def _make_deps(**overrides: Any) -> ChoreographerDeps:
         "blockers_in_lane",
     ):
         getattr(repo, method).return_value = []
+    # C8: default-fresh journal:decision so PM-decision gate passes.
+    # Tests that exercise the gate boundary stub their own value.
+    # The check matches MagicMock and AsyncMock (the two default sentinel
+    # types pytest's unittest.mock leaves on un-stubbed return_values).
+    _ldef = base["journal"].latest_decision_at.return_value
+    if type(_ldef).__name__ in ("MagicMock", "AsyncMock"):
+        base["journal"].latest_decision_at.return_value = datetime.now(UTC)
     return ChoreographerDeps(**base)