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/discourse/functional/_discourse.py

@@ -53,7 +53,7 @@ def mint_admin(domain: str) -> tuple[str, str]:
     cmd = (
         "cd /opt/bitnami/discourse && "
         "RUBY=$(command -v ruby || echo /opt/bitnami/ruby/bin/ruby) && "
-        f"RAILS_ENV=production \"$RUBY\" bin/rails runner \"{_BOOTSTRAP_RB}\""
+        f'RAILS_ENV=production "$RUBY" bin/rails runner "{_BOOTSTRAP_RB}"'
     )
     out = lifecycle.exec_in_app(domain, ["bash", "-c", cmd], service="app", timeout=240)
     key = user = None
@@ -63,9 +63,9 @@ def mint_admin(domain: str) -> tuple[str, str]:
             key = line.split("=", 1)[1].strip()
         elif line.startswith("CCCI_API_USER="):
             user = line.split("=", 1)[1].strip()
-    assert key and user, (
-        f"could not bootstrap discourse admin/API key; rails output tail:\n{out[-1000:]}"
-    )
+    assert (
+        key and user
+    ), f"could not bootstrap discourse admin/API key; rails output tail:\n{out[-1000:]}"
     return key, user