style: repo-wide lint pass — make the lint gate green again

Push builds have been RED on the lint step since ~build 209 from accumulated
formatting drift. This is the mechanical cleanup: ruff format + ruff --fix
(UP038 isinstance unions, SIM105 contextlib.suppress, UP031 f-strings, SIM115
tempfile context manager), shfmt -i 2 -ci, nixpkgs-fmt/statix/deadnix (merged
attrsets, dropped unused lib args), yamllint, and shell quoting fixes in
tests/lasuite-docs/setup_custom_tests.sh. No behaviour changes intended;
lint: PASS, unit tests: 138 passed.

tests/mumble/test_backup.py

@@ -23,6 +23,6 @@ def _sqlite(domain, sql):
 
 
 def test_backup_captures_state(live_app):
-    assert _sqlite(live_app, "SELECT v FROM ci_marker;") == "original", (
-        "the seeded mumble sqlite marker was not present at backup time"
-    )
+    assert (
+        _sqlite(live_app, "SELECT v FROM ci_marker;") == "original"
+    ), "the seeded mumble sqlite marker was not present at backup time"