Toolbox is still being refined; hide it from clients on prod while keeping it
usable on staging. Entry points (header link, dashboard card) render only when
TOOLBOX_VISIBLE=true; a tools/layout redirects /tools/* to /dashboard otherwise.
Routes and ToolUsage table are untouched (no destructive migration).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
