feat(10-04): AdminPage + /admin route + conditional nav entries + e2e spec

- AdminPage: Admin Settings heading, MEMBERS section (avatar+status+action), SHARED CALENDAR radio group + two-tap Save + empty state
- App.tsx: /admin route gated by meQuery.data.user.isAdmin (loading gate prevents flash), SetupBanner mounted above content, BottomTabBar + AppNav receive isAdmin
- AppNav.tsx: ShieldCheck Admin nav entry rendered only when isAdmin=true (D-03 UX gating)
- BottomTabBar.tsx: ShieldCheck Admin tab rendered only when isAdmin=true (D-03 UX gating)
- e2e/admin.spec.ts: 5 assertions across 3 profiles (15 total tests) — admin sees nav+page+members, non-admin: no nav entry + /admin redirects to /calendar
- All 15 e2e tests pass (iphone/pixel/desktop); production build clean

apps/pwa/src/components/AppNav.tsx

@@ -12,7 +12,7 @@
  */
 
 import { NavLink } from 'react-router';
-import { CalendarDays, List } from 'lucide-react';
+import { CalendarDays, List, ShieldCheck } from 'lucide-react';
 import { ColorLegend, type LegendMember } from './ColorLegend.js';
 
 interface AppNavProps {
@@ -21,6 +21,8 @@ interface AppNavProps {
   currentUserName?: string;
   /** Called when the user avatar is tapped — opens the Settings sheet. */
   onOpenSettings?: () => void;
+  /** When true, renders the Admin nav entry (ShieldCheck). UX gating only (D-03). */
+  isAdmin?: boolean;
 }
 
 export function AppNav({
@@ -28,6 +30,7 @@ export function AppNav({
   currentUserColor,
   currentUserName,
   onOpenSettings,
+  isAdmin = false,
 }: AppNavProps) {
   const isMobile = typeof window !== 'undefined' && window.matchMedia('(max-width: 767px)').matches;
 
@@ -47,6 +50,7 @@ export function AppNav({
       currentUserColor={currentUserColor}
       currentUserName={currentUserName}
       onOpenSettings={onOpenSettings}
+      isAdmin={isAdmin}
     />
   );
 }
@@ -129,11 +133,13 @@ function DesktopNav({
   currentUserColor,
   currentUserName,
   onOpenSettings,
+  isAdmin = false,
 }: {
   members: LegendMember[];
   currentUserColor?: string;
   currentUserName?: string;
   onOpenSettings?: () => void;
+  isAdmin?: boolean;
 }) {
   const navLinkStyle = ({ isActive }: { isActive: boolean }): React.CSSProperties => ({
     display: 'flex',
@@ -198,6 +204,13 @@ function DesktopNav({
           <List size={18} aria-hidden="true" />
           Lists
         </NavLink>
+        {/* Admin entry — only when isAdmin=true (UX gating, D-03) */}
+        {isAdmin && (
+          <NavLink to="/admin" style={navLinkStyle} aria-label="Admin settings">
+            <ShieldCheck size={18} aria-hidden="true" />
+            Admin
+          </NavLink>
+        )}
       </div>
 
       {/* Color legend */}

apps/pwa/src/components/BottomTabBar.tsx

@@ -18,7 +18,7 @@
  */
 
 import { NavLink } from 'react-router';
-import { CalendarDays, List } from 'lucide-react';
+import { CalendarDays, List, ShieldCheck } from 'lucide-react';
 
 function isPhone(): boolean {
   return typeof window !== 'undefined' && window.matchMedia('(max-width: 767px)').matches;
@@ -49,7 +49,12 @@ const tabActiveOverride: React.CSSProperties = {
   borderBottom: '2px solid var(--color-member-0)',
 };
 
-export function BottomTabBar() {
+interface BottomTabBarProps {
+  /** When true, renders the Admin tab (ShieldCheck). UX gating only (D-03). */
+  isAdmin?: boolean;
+}
+
+export function BottomTabBar({ isAdmin = false }: BottomTabBarProps) {
   // Phone-only: return null on desktop (≥768px) so the fixed bar does not overlay
   // the AppNav sidebar's Settings/avatar button (FIX 4). Consistent with the
   // isPhone() breakpoint used in AppNav and CalendarShell.
@@ -96,6 +101,21 @@ export function BottomTabBar() {
         <List size={22} aria-hidden="true" />
         <span>Lists</span>
       </NavLink>
+
+      {/* Admin tab — only when isAdmin=true (UX gating, D-03) */}
+      {isAdmin && (
+        <NavLink
+          to="/admin"
+          aria-label="Admin settings"
+          style={({ isActive }) => ({
+            ...tabBase,
+            ...(isActive ? tabActiveOverride : {}),
+          })}
+        >
+          <ShieldCheck size={22} aria-hidden="true" />
+          <span>Admin</span>
+        </NavLink>
+      )}
     </nav>
   );
 }