Tabs gains an `orientation` prop (+ optional per-tab `icon`/`testId`) so the
two hand-rolled NAV tab-sets that duplicated its active treatment now use it:
- SettingsPanel vertical rail (appearance/notifications/account) -> vertical
Tabs with icons; settings-tab-* testIds preserved
- Stats overview/system tabs -> Tabs (rounded-full+border -> the rounded-lg
tab canonical, per the agreed tab shape)
The underline ChannelPage tabs and the icon NavSidebar rail are intentionally
left as distinct idioms. Self-E2E'd: settings rail switches + persists with
icons, stats tabs toggle. gate green (tsc/eslint-0/vitest 136/knip/prettier).
Branch not merged.