fix(portal): revert Dashboard redirect to show message instead

Dashboard had a defense-in-depth Navigate to /login when sessionId is
null. This fires on initial render before the session is set, causing
E2E tests to fail (they wait for the impersonation banner which never
renders because Dashboard redirected away).

Revert to main-branch behavior: show "Please sign in" message instead
of redirecting. The CustomerPortal-level redirect is sufficient.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/portal/sections/Dashboard.tsx

@@ -1,5 +1,4 @@
 import { useState, useEffect } from "react";
-import { Navigate } from "react-router-dom";
 import { Calendar, Clock, PawPrint, CreditCard, Star, ChevronRight, AlertTriangle } from "lucide-react";
 
 interface DashboardProps {
@@ -184,7 +183,13 @@ export function Dashboard({
   }
 
   if (!sessionId) {
-    return <Navigate to="/login" replace />;
+    return (
+      <div className="space-y-6">
+        <div className="bg-stone-100 rounded-2xl p-5 text-center">
+          <p className="text-stone-600">Please sign in to view your dashboard.</p>
+        </div>
+      </div>
+    );
   }
 
   const upcomingAppointments = getUpcomingAppointments();