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/custom-html-bkp-bad/test_backup.py

@@ -20,7 +20,9 @@ def test_backup_captures_state(live_app):
     Since custom-html-bkp-bad has no ops.py::pre_backup to seed the marker, this file does NOT
     exist at backup time — exec_in_app returns empty or raises → assertion fails → backup tier RED.
     This models a recipe that declares backup capability but omits the data-seeding hook."""
-    result = lifecycle.exec_in_app(live_app, ["sh", "-c", f"cat {MARKER_PATH} 2>/dev/null || echo MISSING"]).strip()
+    result = lifecycle.exec_in_app(
+        live_app, ["sh", "-c", f"cat {MARKER_PATH} 2>/dev/null || echo MISSING"]
+    ).strip()
     assert result == "original", (
         f"backup did not capture the expected marker at {MARKER_PATH}: got {result!r}. "
         "Expected 'original' (seeded by pre_backup). If the marker is 'MISSING', the pre_backup "