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-tiny/functional/test_serves_content.py

@@ -79,9 +79,9 @@ def test_static_file_roundtrip_and_404(live_app):
         # A random non-existent path must 404 — proves real static-file semantics, distinguishing a
         # working server from a 200-everything stub or a mis-routed Traefik fallback.
         miss_status, _ = _get(f"https://{live_app}/ccci-missing-{uuid.uuid4().hex}.txt")
-        assert miss_status == 404, (
-            f"missing path returned {miss_status} (expected 404 — generic 200-returner / mis-route?)"
-        )
+        assert (
+            miss_status == 404
+        ), f"missing path returned {miss_status} (expected 404 — generic 200-returner / mis-route?)"
     finally:
         with contextlib.suppress(OSError):
             os.remove(path)