feat(tui): read display.streaming / show_reasoning / show_cost / inline_diffs from config

Extends ConfigDisplayConfig and UiState so the four new display flags
flow from `config.get {key:"full"}` into the nanostore. applyDisplay is
exported to keep the fan-out testable without an Ink harness.

Defaults mirror v1 parity: streaming + inline_diffs default true
(opt-out via `=== false`), show_cost + show_reasoning default false
(opt-in via plain truthy check).

ui-tui/src/__tests__/useConfigSync.test.ts

@@ -0,0 +1,67 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { $uiState, resetUiState } from '../app/uiStore.js'
+import { applyDisplay } from '../app/useConfigSync.js'
+
+describe('applyDisplay', () => {
+  beforeEach(() => {
+    resetUiState()
+  })
+
+  it('fans every display flag out to $uiState and the bell callback', () => {
+    const setBell = vi.fn()
+
+    applyDisplay(
+      {
+        config: {
+          display: {
+            bell_on_complete: true,
+            details_mode: 'expanded',
+            inline_diffs: false,
+            show_cost: true,
+            show_reasoning: true,
+            streaming: false,
+            tui_compact: true,
+            tui_statusbar: false
+          }
+        }
+      },
+      setBell
+    )
+
+    const s = $uiState.get()
+    expect(setBell).toHaveBeenCalledWith(true)
+    expect(s.compact).toBe(true)
+    expect(s.detailsMode).toBe('expanded')
+    expect(s.inlineDiffs).toBe(false)
+    expect(s.showCost).toBe(true)
+    expect(s.showReasoning).toBe(true)
+    expect(s.statusBar).toBe(false)
+    expect(s.streaming).toBe(false)
+  })
+
+  it('applies v1 parity defaults when display fields are missing', () => {
+    const setBell = vi.fn()
+
+    applyDisplay({ config: { display: {} } }, setBell)
+
+    const s = $uiState.get()
+    expect(setBell).toHaveBeenCalledWith(false)
+    expect(s.inlineDiffs).toBe(true)
+    expect(s.showCost).toBe(false)
+    expect(s.showReasoning).toBe(false)
+    expect(s.statusBar).toBe(true)
+    expect(s.streaming).toBe(true)
+  })
+
+  it('treats a null config like an empty display block', () => {
+    const setBell = vi.fn()
+
+    applyDisplay(null, setBell)
+
+    const s = $uiState.get()
+    expect(setBell).toHaveBeenCalledWith(false)
+    expect(s.inlineDiffs).toBe(true)
+    expect(s.streaming).toBe(true)
+  })
+})