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/mattermost-lts/functional/test_health_check.py

@@ -18,9 +18,7 @@ from harness import http as harness_http  # noqa: E402
 def test_root_serves(live_app):
     """GET / → 200 or 302 (mattermost web app shell / login redirect)."""
     url = f"https://{live_app}/"
-    status, _ = harness_http.retry_http_get(
-        url, expect_status=(200, 302), max_wait=60, interval=3
-    )
+    status, _ = harness_http.retry_http_get(url, expect_status=(200, 302), max_wait=60, interval=3)
     assert status in (200, 302), f"GET {url} HTTP {status} (expected 200/302)"
 
 
@@ -28,10 +26,8 @@ def test_system_ping_ok(live_app):
     """GET /api/v4/system/ping → 200 with JSON {"status":"OK"} — the mattermost server's own
     liveness endpoint (distinguishes a live mattermost API from a Traefik fallback / dead backend)."""
     url = f"https://{live_app}/api/v4/system/ping"
-    status, body = harness_http.retry_http_get(
-        url, expect_status=200, max_wait=120, interval=3
-    )
+    status, body = harness_http.retry_http_get(url, expect_status=200, max_wait=120, interval=3)
     assert status == 200, f"GET {url} HTTP {status} (expected 200)"
-    assert isinstance(body, dict) and body.get("status") == "OK", (
-        f"/api/v4/system/ping did not report status=OK; got {body!r}"
-    )
+    assert (
+        isinstance(body, dict) and body.get("status") == "OK"
+    ), f"/api/v4/system/ping did not report status=OK; got {body!r}"