Add an optional `tab` search param (validated against the known tab set) to /dashboard/settings and drive the Tabs component from it, so each tab is shareable/bookmarkable (e.g. /dashboard/settings?tab=referral). Tab clicks update the URL with replace to avoid history spam; existing links need no search param since `tab` is optional. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>