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/turnController.ts

@@ -11,7 +11,7 @@ import type { ActiveTool, ActivityItem, Msg, SubagentProgress } from '../types.j
 
 import { resetOverlayState } from './overlayStore.js'
 import { patchTurnState, resetTurnState } from './turnStore.js'
-import { patchUiState } from './uiStore.js'
+import { getUiState, patchUiState } from './uiStore.js'
 
 const INTERRUPT_COOLDOWN_MS = 1500
 const ACTIVITY_LIMIT = 8
@@ -226,10 +226,17 @@ class TurnController {
     }
 
     this.bufRef = rendered ?? this.bufRef + text
-    this.scheduleStreaming()
+
+    if (getUiState().streaming) {
+      this.scheduleStreaming()
+    }
   }
 
   recordReasoningAvailable(text: string) {
+    if (!getUiState().showReasoning) {
+      return
+    }
+
     const incoming = text.trim()
 
     if (!incoming || this.reasoningText.trim()) {
@@ -242,6 +249,10 @@ class TurnController {
   }
 
   recordReasoningDelta(text: string) {
+    if (!getUiState().showReasoning) {
+      return
+    }
+
     this.reasoningText += text
     this.scheduleReasoning()
     this.pulseReasoningStreaming()