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/functional/test_server_config_limits.py

@@ -32,6 +32,7 @@ def test_configured_max_users_surfaces_in_serverconfig(live_app):
     )
     # allow_html defaults true in the recipe; assert it is present/boolean to prove the field set
     # is the real ServerConfig (not an empty/garbled decode).
-    assert cfg.get("allow_html") in (0, 1), (
-        f"ServerConfig.allow_html unexpected: {cfg.get('allow_html')!r}"
-    )
+    assert cfg.get("allow_html") in (
+        0,
+        1,
+    ), f"ServerConfig.allow_html unexpected: {cfg.get('allow_html')!r}"