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/__tests__/createGatewayEventHandler.test.ts

@@ -4,7 +4,7 @@ import { createGatewayEventHandler } from '../app/createGatewayEventHandler.js'
 import { resetOverlayState } from '../app/overlayStore.js'
 import { turnController } from '../app/turnController.js'
 import { resetTurnState } from '../app/turnStore.js'
-import { resetUiState } from '../app/uiStore.js'
+import { patchUiState, resetUiState } from '../app/uiStore.js'
 import { estimateTokensRough } from '../lib/text.js'
 import type { Msg } from '../types.js'
 
@@ -47,6 +47,7 @@ describe('createGatewayEventHandler', () => {
     resetUiState()
     resetTurnState()
     turnController.fullReset()
+    patchUiState({ showReasoning: true })
   })
 
   it('persists completed tool rows when message.complete lands immediately after tool.complete', () => {