docs(6209): test prose in the present tense — "used to", "previously", "before this" restated as the failure shape

Twenty-eight test files described the code they guard by what it did
before a fix. Each is now the property and the failure it prevents, in the
present tense: the backfill snapshot, the per-dial calibration query, the
rule scope, the lesson trigger filter, the subshell global, the trash owner
scope, the version readout fallback, and others. A docstring line that
narrated the backup suite's own history is removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_integration_backup_note_roundtrip.py

@@ -29,7 +29,7 @@ RESTORED_USERNAME = "backup_roundtrip_restored"
 @pytest_asyncio.fixture
 async def source():
     """A snippet, a process, and an issue that arose from a work task — the
-    shapes whose identity the backup used to drop — exported as backup rows.
+    shapes whose identity a backup can drop — exported as backup rows.
 
     Deleted children-first: `arose_from_id` is a real FK, so removing the
     origin while the issue still points at it is asking the database a