chore: additional AI slop cleanup and enforcer wiring from sessions 1/5

Session 1 (ses_2ad65873): with_enforcer builders + 2 regression tests
Session 5 (ses_2ad67e8e): continued AI slop cleanup pass — redundant
  comments, unused_self suppressions, unreachable! tightening
Session cleanup (ses_2ad6b26c): Python placeholder centralization

Workspace tests: 363+ passed, 0 failed.

src/_archive_helper.py

@@ -0,0 +1,17 @@
+"""Shared helper for archive placeholder packages."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+
+def load_archive_metadata(package_name: str) -> dict:
+    """Load archive metadata from reference_data/subsystems/{package_name}.json."""
+    snapshot_path = (
+        Path(__file__).resolve().parent
+        / "reference_data"
+        / "subsystems"
+        / f"{package_name}.json"
+    )
+    return json.loads(snapshot_path.read_text())