weichen
abc1a6d784
Why: the backend startup layer had only defaults and CLI flags; the configuration standard's baseline (file, env, CLI layers, read-only explain, instance isolation) requires the full pipe for dev/test/prod operation. Evidence: fields and categories mapped one-to-one onto the existing app Options; runtime settings API kept as the separate business-policy layer. Impact: design record only; implementation follows in the backend repo. Refs: standards/configuration.md; backend feature/config-surface