test(backup): assert the version constant, not a copy of it

The export test pinned `out["version"] == 4`, so bumping BACKUP_VERSION broke a
test that was only ever checking the payload carries the version — which it
still did. Asserts against backup.BACKUP_VERSION now, and covers the six v5
sections alongside the v3 ones.

The guard itself passed on the first run: every table in Base.metadata was
accounted for, in both directions.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UaYUaouG9jjhATyuxCKrQs

tests/test_services_backup.py

@@ -95,16 +95,18 @@ class _CM:
 
 
 @pytest.mark.asyncio
-async def test_export_full_backup_contains_v3_sections():
+async def test_export_full_backup_contains_every_declared_section():
     with patch("scribe.services.backup.async_session", lambda: _CM()):
         out = await backup.export_full_backup()
 
-    assert out["version"] == 4
+    assert out["version"] == backup.BACKUP_VERSION
     assert out["scope"] == "full"
     assert "api_keys" in out["_not_included"]
-    # The sections v2 silently dropped must now be present (empty here).
+    # The sections v2 silently dropped, plus the six v5 added (empty here).
     for key in ("rulebooks", "rulebook_topics", "rules",
                 "rulebook_subscriptions", "rule_suppressions",
-                "topic_suppressions"):
-        assert key in out, f"missing v3 section: {key}"
+                "topic_suppressions",
+                "systems", "record_systems", "design_systems",
+                "design_tokens", "note_usage_events", "repo_bindings"):
+        assert key in out, f"missing export section: {key}"
         assert out[key] == []