Deduplicate the "save a workspace setting" plumbing shared by HtmlEmbedSettings
and TrackerSettings (workspace atom read, isLoading state, updateWorkspace + atom
merge forcing settings[key], success/error notifications) into a new
feature-scoped hook useWorkspaceSetting(key).
- Each component keeps its own interaction model: html-embed is an optimistic
toggle with revert-on-failure; tracker is edit-then-save on an explicit button.
- Unify error handling on the better pattern: surface err.response?.data?.message
and use console.error (html-embed previously used console.log + a generic message).
No user-facing behavior change; client typecheck clean.
Test-coverage follow-ups (untested trackerHead injection in ShareSeoController and
the no-op audit branch) tracked in #100.