feat: persist collapsible app sidebar

src/components/shell/AppShellLayout.tsx

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+import type { ReactNode } from 'react';
+import { AppSidebar } from './AppSidebar';
+
+export function AppShellLayout({ children }: { children: ReactNode }) {
+  return (
+    <div className="flex min-h-screen bg-[#050505]">
+      <AppSidebar />
+      <main className="min-w-0 flex-1">{children}</main>
+    </div>
+  );
+}

src/components/shell/AppSidebar.test.tsx

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+/** @vitest-environment happy-dom */
+
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { cleanup, fireEvent, render, screen } from '@testing-library/react';
+import { AppSidebar } from './AppSidebar';
+
+vi.mock('next/navigation', () => ({ usePathname: () => '/analytics' }));
+
+describe('AppSidebar', () => {
+  afterEach(() => {
+    cleanup();
+    localStorage.clear();
+  });
+
+  it('persists collapsed state and keeps labels accessible', () => {
+    render(<AppSidebar />);
+    const toggle = screen.getByRole('button', { name: 'Collapse sidebar' });
+
+    fireEvent.click(toggle);
+
+    expect(screen.getByRole('button', { name: 'Expand sidebar' })).toHaveAttribute(
+      'aria-expanded',
+      'false',
+    );
+    expect(screen.getByRole('link', { name: 'Analytics' })).toHaveAttribute('title', 'Analytics');
+    expect(localStorage.getItem('commitlabs:sidebar-collapsed')).toBe('true');
+  });
+
+  it('marks the active route', () => {
+    render(<AppSidebar />);
+    expect(screen.getByRole('link', { name: 'Analytics' })).toHaveAttribute('aria-current', 'page');
+  });
+});

src/components/shell/AppSidebar.tsx

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+'use client';
+
+import Link from 'next/link';
+import { usePathname } from 'next/navigation';
+import { useEffect, useState } from 'react';
+import { FiBarChart2, FiChevronLeft, FiHome, FiMenu, FiPlus, FiSettings } from 'react-icons/fi';
+
+const STORAGE_KEY = 'commitlabs:sidebar-collapsed';
+
+const navigation = [
+  { href: '/', label: 'Overview', icon: FiHome },
+  { href: '/analytics', label: 'Analytics', icon: FiBarChart2 },
+  { href: '/create', label: 'Create commitment', icon: FiPlus },
+  { href: '/settings', label: 'Settings', icon: FiSettings },
+] as const;
+
+export function AppSidebar() {
+  const pathname = usePathname();
+  const [collapsed, setCollapsed] = useState(false);
+  const [hydrated, setHydrated] = useState(false);
+
+  useEffect(() => {
+    setCollapsed(window.localStorage.getItem(STORAGE_KEY) === 'true');
+    setHydrated(true);
+  }, []);
+
+  useEffect(() => {
+    if (hydrated) window.localStorage.setItem(STORAGE_KEY, String(collapsed));
+  }, [collapsed, hydrated]);
+
+  return (
+    <aside
+      aria-label="Application navigation"
+      className={`hidden min-h-screen shrink-0 border-r border-white/10 bg-[#0a0a0b] transition-[width] md:block ${
+        collapsed ? 'w-16' : 'w-64'
+      }`}
+    >
+      <div className="sticky top-0 flex min-h-screen flex-col p-3">
+        <button
+          type="button"
+          aria-label={collapsed ? 'Expand sidebar' : 'Collapse sidebar'}
+          aria-expanded={!collapsed}
+          onClick={() => setCollapsed((value) => !value)}
+          className="mb-5 flex h-10 items-center justify-center rounded-lg text-white/70 hover:bg-white/10 hover:text-white"
+        >
+          {collapsed ? <FiMenu aria-hidden="true" /> : <FiChevronLeft aria-hidden="true" />}
+        </button>
+
+        <nav aria-label="Primary" className="space-y-2">
+          {navigation.map(({ href, label, icon: Icon }) => {
+            const active = pathname === href || (href !== '/' && pathname.startsWith(`${href}/`));
+            return (
+              <Link
+                key={href}
+                href={href}
+                aria-current={active ? 'page' : undefined}
+                aria-label={collapsed ? label : undefined}
+                title={collapsed ? label : undefined}
+                className={`flex items-center gap-3 rounded-lg px-3 py-2 text-sm ${
+                  active ? 'bg-cyan-400/15 text-cyan-300' : 'text-white/70 hover:bg-white/10'
+                }`}
+              >
+                <Icon aria-hidden="true" />
+                {!collapsed && <span>{label}</span>}
+              </Link>
+            );
+          })}
+        </nav>
+      </div>
+    </aside>
+  );
+}

src/components/shell/index.ts

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+export { AppShellLayout } from './AppShellLayout';
+export { AppSidebar } from './AppSidebar';