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/app/createGatewayEventHandler.ts

@@ -266,7 +266,7 @@ export function createGatewayEventHandler(ctx: GatewayEventHandlerContext): (ev:
       case 'tool.complete':
         turnController.recordToolComplete(ev.payload.tool_id, ev.payload.name, ev.payload.error, ev.payload.summary)
 
-        if (ev.payload.inline_diff) {
+        if (ev.payload.inline_diff && getUiState().inlineDiffs) {
           sys(ev.payload.inline_diff)
         }