Foundation for the Config split. UserEntry / ConfigData move out
of the page so the upcoming hook + tab extractions can import
without reaching back through Config.tsx. New ConfigTab union and
FormMsg type for the inline success/error chip pattern that
repeats across every admin form on the page.
- New Config/types.ts (UserEntry, ConfigData, ConfigTab, FormMsg)
- Config.tsx loses the inline interfaces and the `as any` cast on
setActiveTab in the tab-switcher.
