Integration test driving the real bridge _save() and engine
_resolve_output_language(): a language chosen in the settings UI is written to
both the persistent volume and the runtime config, applies immediately (config
wins over the OUTPUT_LANGUAGE env), and survives a simulated container recreate
(entrypoint re-renders the config then merges the persistent override). Also
asserts the persona and reply directive both follow the persisted language.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
