feat(28-03): add profile navigation link and extend /me with createdAt

Adds Profile link to UserMenu dropdown (above Settings), extends /me
endpoint to return user's createdAt for member-since display, and
updates AuthState interface with optional createdAt field.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/components/UserMenu.tsx

@@ -30,6 +30,18 @@ export function UserMenu() {
 			</button>
 			{open && (
 				<div className="absolute right-0 mt-1 w-40 bg-white rounded-lg shadow-lg border border-gray-200 py-1 z-50">
+					<Link
+						to="/profile"
+						onClick={() => setOpen(false)}
+						className="flex items-center gap-2 px-3 py-2 text-sm text-gray-700 hover:bg-gray-50 transition-colors"
+					>
+						<LucideIcon
+							name="circle-user"
+							size={16}
+							className="text-gray-400"
+						/>
+						Profile
+					</Link>
 					<Link
 						to="/settings"
 						onClick={() => setOpen(false)}

src/client/hooks/useAuth.ts

@@ -2,7 +2,7 @@ import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import { apiDelete, apiGet, apiPost } from "../lib/api";
 
 interface AuthState {
-	user: { id: string; email?: string } | null;
+	user: { id: string; email?: string; createdAt?: string } | null;
 	authenticated: boolean;
 }