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_version_readout.py

@@ -33,11 +33,11 @@ def test_something_actually_reads_the_version_endpoint():
 
 
 def test_the_footer_does_not_default_to_a_plausible_version():
-    """The regression this readout was built to remove.
+    """A failed fetch does not render a plausible version.
 
-    `appVersion` used to start life as the literal `"dev"` and the fetch
-    swallowed its own failure, so an instance that could not answer rendered
-    exactly what a healthy local build renders. Two very different states, one
+    If `appVersion` starts life as the literal `"dev"` and the fetch swallows
+    its own failure, an instance that cannot answer renders exactly what a
+    healthy local build renders. Two very different states, one
     string, and no way to tell them apart from the page.
 
     Pinned as "the ref does not start at a version-shaped literal" rather than