feat(renderer): Zen mode (Esc exits, hides chrome)

tests/unit/hooks/use-zen-mode.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { renderHook } from '@testing-library/react';
+import { useZenMode } from '@/hooks/use-zen-mode';
+import { useAppStore } from '@/stores/app-store';
+
+describe('useZenMode', () => {
+  beforeEach(() => {
+    localStorage.clear();
+    useAppStore.setState({ ...useAppStore.getInitialState(), zenMode: true });
+  });
+
+  it('attaches a keydown listener that exits zen mode on Escape', () => {
+    renderHook(() => useZenMode());
+    expect(useAppStore.getState().zenMode).toBe(true);
+
+    // Simulate Escape keydown
+    const event = new KeyboardEvent('keydown', { key: 'Escape' });
+    window.dispatchEvent(event);
+
+    expect(useAppStore.getState().zenMode).toBe(false);
+  });
+
+  it('does nothing if zen mode is already off', () => {
+    useAppStore.setState({ ...useAppStore.getInitialState(), zenMode: false });
+    const setZenMode = vi.fn();
+    useAppStore.setState({ setZenMode });
+    renderHook(() => useZenMode());
+    // No Escape dispatched; setZenMode should not be called
+    expect(setZenMode).not.toHaveBeenCalled();
+  });
+});