feat(tui): honor display.* flags in turn renderer, status bar, and event handler

- turnController gates scheduleStreaming / reasoning recorders on
  streaming + showReasoning so disabling them keeps the buffer silent
  until message.complete flushes
- createGatewayEventHandler only surfaces inline_diff previews when
  inlineDiffs is on
- StatusRule takes a showCost prop and renders `· $X.XXXX` with the
  same toFixed(4) formatting as /usage when usage.cost_usd is present
- Usage grows cost_usd?: number to match the gateway payload
- Existing handler tests flip showReasoning on in beforeEach so
  reasoning-flow assertions keep their meaning

ui-tui/src/components/appLayout.tsx

@@ -190,6 +190,7 @@ const ComposerPane = memo(function ComposerPane({
             cwdLabel={status.cwdLabel}
             model={ui.info?.model?.split('/').pop() ?? ''}
             sessionStartedAt={status.sessionStartedAt}
+            showCost={ui.showCost}
             status={ui.status}
             statusColor={status.statusColor}
             t={ui.theme}