[Doyoubelieveinfate]

Prepared with Codex at @Doyoubelieveinfate's request.

Fixes #1978.

With stdout redirected, http -qq --check-status URL > output still prints HTTP status warnings because log_error() bypasses the quiet threshold when stdout is not a TTY. Apply the threshold regardless of stdout redirection. A single -q still displays warnings; errors and exit codes are preserved.

Update the redirected-output regression test for both -qq and --quiet --quiet, assert the HTTP error exit code, and check that errors remain visible with either terminal or redirected output.

Validation on Python 3.13.5:

• The two warning-suppression cases fail before the fix and pass afterward.
• Output, error, and session suites: 196 passed, 3 expected failures.
• Real CLI subprocesses against a local HTTP 500 server: -qq suppresses warnings while keeping exit code 5; -q retains warnings. An invalid URL still prints an error and exits 1.
• make codestyle VENV_ROOT=.venv and git diff --check pass.

CI note: the Ubuntu/Python 3.7 jobs fail in actions/setup-python, before running tests, because Python 3.7 is unavailable for Ubuntu 24.04 (job log). The code-style and documentation checks pass.