feat: Phase 5 stabilization schedules and custodian path URIs

Add phase5_stabilization_check State Hub resolver with progress evidence
sinks, schedule projections for daily and closeout checks, custodian:// and
activity-core:// runtime path resolution, and Railiance mounts under /var/custodian.

src/activity_core/rules/executor.py

@@ -799,7 +799,9 @@ def _load_output_schema(schema_path: str) -> dict[str, Any] | None:
     if not schema_path:
         return None
 
-    path = Path(schema_path)
+    from activity_core.runtime_paths import resolve_runtime_path
+
+    path = resolve_runtime_path(schema_path)
     if not path.exists():
         return None