feat(renderer): AppShell with resizable panes, sidebar/preview toggle, persisted sizes

tests/component/layout/AppShell.test.tsx

@@ -0,0 +1,49 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { render, screen } from '@testing-library/react';
+import { ThemeProvider } from '@/components/theme-provider';
+import { AppShell } from '@/components/layout/AppShell';
+import { useAppStore } from '@/stores/app-store';
+
+// Mock react-resizable-panels for jsdom environment
+vi.mock('@/components/ui/resizable', () => ({
+  ResizablePanelGroup: ({ children, direction, onLayout }: any) => (
+    <div data-testid="resizable-panel-group" data-direction={direction}>
+      {children}
+    </div>
+  ),
+  ResizablePanel: ({ children, defaultSize, minSize, maxSize }: any) => (
+    <div data-testid="resizable-panel" data-size={defaultSize} data-min={minSize} data-max={maxSize}>
+      {children}
+    </div>
+  ),
+  ResizableHandle: () => <div data-testid="resizable-handle" />,
+}));
+
+describe('AppShell', () => {
+  beforeEach(() => {
+    localStorage.clear();
+    useAppStore.setState({ sidebarVisible: true, previewVisible: true, zenMode: false });
+  });
+
+  it('renders all shell surfaces when sidebar and preview are visible', () => {
+    render(
+      <ThemeProvider defaultTheme="dark" attribute="class">
+        <AppShell />
+      </ThemeProvider>
+    );
+    expect(screen.getByText(/markdownconverter/i)).toBeInTheDocument();
+    expect(screen.getByText(/no files open/i)).toBeInTheDocument();
+    expect(screen.getByText(/no file selected/i)).toBeInTheDocument();
+    expect(screen.getByText(/0 words/i)).toBeInTheDocument();
+  });
+
+  it('hides sidebar when sidebarVisible is false', () => {
+    useAppStore.setState({ sidebarVisible: false });
+    render(
+      <ThemeProvider defaultTheme="dark" attribute="class">
+        <AppShell />
+      </ThemeProvider>
+    );
+    expect(screen.queryByText(/file tree placeholder/i)).not.toBeInTheDocument();
+  });
+});