feat: add AppShell with persistent icon sidebar and mobile bottom tab bar

src/components/ui/AppShell.tsx

@@ -0,0 +1,19 @@
+// NOTE: intentionally no 'use client' — must remain a Server Component
+import { Sidebar } from './Sidebar';
+
+interface AppShellProps {
+  children: React.ReactNode;
+  showUsers: boolean;
+}
+
+export function AppShell({ children, showUsers }: AppShellProps) {
+  return (
+    <div className="min-h-screen bg-gh-base">
+      <Sidebar showUsers={showUsers} />
+      {/* Offset for sidebar (desktop: left margin, mobile: bottom padding) */}
+      <div className="pb-14 md:pb-0 md:pl-14">
+        {children}
+      </div>
+    </div>
+  );
+}

src/components/ui/Sidebar.tsx

@@ -0,0 +1,94 @@
+'use client';
+
+import Link from 'next/link';
+import { usePathname } from 'next/navigation';
+import { cn } from '@/lib/utils';
+
+interface SidebarProps {
+  showUsers: boolean; // true if user has membership.view permission
+}
+
+function ServerIcon({ active }: { active: boolean }) {
+  return (
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={2} className={cn('h-5 w-5', active ? 'text-gh-blue' : 'text-gh-subtle')}>
+      <rect x="2" y="3" width="20" height="5" rx="1" />
+      <rect x="2" y="10" width="20" height="5" rx="1" />
+      <rect x="2" y="17" width="20" height="5" rx="1" />
+      <circle cx="6" cy="5.5" r="1" fill="currentColor" />
+      <circle cx="6" cy="12.5" r="1" fill="currentColor" />
+      <circle cx="6" cy="19.5" r="1" fill="currentColor" />
+    </svg>
+  );
+}
+
+function UsersIcon({ active }: { active: boolean }) {
+  return (
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth={2} className={cn('h-5 w-5', active ? 'text-gh-blue' : 'text-gh-subtle')}>
+      <path d="M17 21v-2a4 4 0 00-4-4H5a4 4 0 00-4 4v2" />
+      <circle cx="9" cy="7" r="4" />
+      <path d="M23 21v-2a4 4 0 00-3-3.87M16 3.13a4 4 0 010 7.75" />
+    </svg>
+  );
+}
+
+export function Sidebar({ showUsers }: SidebarProps) {
+  const pathname = usePathname();
+  const isServers = !pathname.startsWith('/dashboard/membership');
+  const isUsers = pathname.startsWith('/dashboard/membership');
+
+  const navItems = [
+    { href: '/dashboard', label: 'Servers', active: isServers, icon: <ServerIcon active={isServers} /> },
+    ...(showUsers ? [{ href: '/dashboard/membership', label: 'Users', active: isUsers, icon: <UsersIcon active={isUsers} /> }] : []),
+  ];
+
+  return (
+    <>
+      {/* Desktop icon sidebar */}
+      <aside className="fixed inset-y-0 left-0 z-40 hidden w-14 flex-col items-center border-r border-gh-border-muted bg-gh-sidebar py-3 md:flex">
+        {/* Logo */}
+        <div className="mb-4 flex h-8 w-8 items-center justify-center rounded-lg bg-gh-blue">
+          <svg viewBox="0 0 24 24" fill="none" stroke="#0d1117" strokeWidth={2.5} className="h-4 w-4">
+            <path d="M12 2L2 7l10 5 10-5-10-5zM2 17l10 5 10-5M2 12l10 5 10-5" />
+          </svg>
+        </div>
+
+        {/* Nav icons */}
+        <nav className="flex flex-1 flex-col items-center gap-1">
+          {navItems.map((item) => (
+            <Link
+              key={item.href}
+              href={item.href}
+              title={item.label}
+              className={cn(
+                'flex h-9 w-9 items-center justify-center rounded-lg transition-colors',
+                item.active ? 'bg-gh-blue-bg' : 'hover:bg-gh-overlay'
+              )}
+            >
+              {item.icon}
+            </Link>
+          ))}
+        </nav>
+
+        {/* Avatar placeholder */}
+        <div className="mt-auto h-7 w-7 rounded-full border-2 border-gh-border bg-gh-overlay" />
+      </aside>
+
+      {/* Mobile bottom tab bar */}
+      <nav className="fixed inset-x-0 bottom-0 z-40 flex h-14 items-center justify-around border-t border-gh-border-muted bg-gh-sidebar md:hidden">
+        {navItems.map((item) => (
+          <Link
+            key={item.href}
+            href={item.href}
+            className={cn(
+              'flex flex-col items-center justify-center gap-0.5 px-4 py-2 text-xs transition-colors',
+              item.active ? 'text-gh-blue' : 'text-gh-subtle'
+            )}
+          >
+            {item.icon}
+            <span>{item.label}</span>
+          </Link>
+        ))}
+      </nav>
+    </>
+  );
+}