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/functional/test_content_roundtrip.py

@@ -15,7 +15,8 @@ import sys
 import uuid
 
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "runner"))
-from harness import http as harness_http, lifecycle  # noqa: E402
+from harness import http as harness_http  # noqa: E402
+from harness import lifecycle
 
 
 def test_content_roundtrip(live_app):

tests/custom-html/functional/test_content_type_header.py

@@ -53,9 +53,9 @@ def test_content_type_html_and_txt(live_app):
     ct_txt = h_txt.get("content-type", "")
 
     # nginx default: "text/html" for .html and "text/plain" for .txt (may include "; charset=utf-8")
-    assert ct_html.startswith("text/html"), (
-        f"{html_name} Content-Type={ct_html!r}, expected text/html (nginx MIME config broken?)"
-    )
-    assert ct_txt.startswith("text/plain"), (
-        f"{txt_name} Content-Type={ct_txt!r}, expected text/plain (nginx MIME config broken?)"
-    )
+    assert ct_html.startswith(
+        "text/html"
+    ), f"{html_name} Content-Type={ct_html!r}, expected text/html (nginx MIME config broken?)"
+    assert ct_txt.startswith(
+        "text/plain"
+    ), f"{txt_name} Content-Type={ct_txt!r}, expected text/plain (nginx MIME config broken?)"