feat: modernize login page with dark theme and breathing logo animation

- Dark gradient background (slate-950/blue-950) with ambient blur effects
- Circular logo centered with dual-ring frosted glass design
- Heartbeat breathing animation (3s cycle) with glow pulse on outer ring
- Gradient sign-in button with hover shadow effects
- Removed "first user" warning, replaced with subtle "authorized personnel" note
- Closes #5 and #6

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

frontend/src/pages/Login.tsx

@@ -1,7 +1,7 @@
 import { useEffect } from 'react';
 import { useNavigate } from 'react-router-dom';
 import { useAuth } from '@/contexts/AuthContext';
-import { Plane } from 'lucide-react';
+import { Plane, LogIn, Shield } from 'lucide-react';
 
 export function Login() {
   const { isAuthenticated, loginWithRedirect } = useAuth();
@@ -14,30 +14,51 @@ export function Login() {
   }, [isAuthenticated, navigate]);
 
   return (
-    <div className="min-h-screen flex items-center justify-center bg-gradient-to-br from-primary/5 via-background to-primary/10">
-      <div className="max-w-md w-full bg-card border border-border rounded-lg shadow-xl p-8">
-        <div className="text-center mb-8">
-          <div className="inline-block p-3 bg-primary/10 rounded-full mb-4">
-            <Plane className="h-12 w-12 text-primary" />
+    <div className="min-h-screen flex items-center justify-center relative overflow-hidden bg-gradient-to-br from-slate-950 via-slate-900 to-blue-950">
+      {/* Background ambient effects */}
+      <div className="absolute inset-0 overflow-hidden">
+        <div className="absolute -top-1/2 -left-1/2 w-full h-full bg-gradient-radial from-blue-500/10 to-transparent rounded-full blur-3xl" />
+        <div className="absolute -bottom-1/2 -right-1/2 w-full h-full bg-gradient-radial from-indigo-500/8 to-transparent rounded-full blur-3xl" />
+        <div className="absolute top-1/4 right-1/4 w-96 h-96 bg-blue-500/5 rounded-full blur-3xl" />
+      </div>
+
+      {/* Content */}
+      <div className="relative z-10 flex flex-col items-center gap-10 px-4 w-full max-w-sm">
+        {/* Breathing logo circle */}
+        <div className="animate-heartbeat">
+          <div className="relative w-36 h-36 rounded-full bg-gradient-to-br from-blue-500/20 to-indigo-600/20 backdrop-blur-sm border border-white/10 flex items-center justify-center animate-glow-pulse">
+            {/* Inner circle */}
+            <div className="w-28 h-28 rounded-full bg-gradient-to-br from-blue-500/30 to-indigo-600/30 border border-white/10 flex items-center justify-center shadow-2xl">
+              <Plane className="h-14 w-14 text-blue-400 drop-shadow-lg" />
+            </div>
           </div>
-          <h1 className="text-3xl font-bold text-foreground mb-2">
+        </div>
+
+        {/* Title */}
+        <div className="text-center">
+          <h1 className="text-4xl font-bold text-white tracking-tight mb-2">
             VIP Coordinator
           </h1>
-          <p className="text-muted-foreground">
-            Transportation logistics and event coordination
+          <p className="text-blue-200/60 text-sm tracking-wide">
+            Transportation logistics & event coordination
           </p>
         </div>
 
-        <button
-          onClick={() => loginWithRedirect()}
-          className="w-full bg-primary text-primary-foreground py-3 px-4 rounded-lg font-medium hover:bg-primary/90 transition-colors"
-        >
-          Sign In with Auth0
-        </button>
+        {/* Sign in card */}
+        <div className="w-full">
+          <button
+            onClick={() => loginWithRedirect()}
+            className="w-full group relative flex items-center justify-center gap-3 bg-gradient-to-r from-blue-600 to-indigo-600 text-white py-4 px-6 rounded-2xl font-semibold text-lg shadow-lg shadow-blue-500/25 hover:shadow-blue-500/40 hover:from-blue-500 hover:to-indigo-500 active:scale-[0.98] transition-all duration-200"
+          >
+            <LogIn className="h-5 w-5 transition-transform group-hover:-translate-x-0.5" />
+            Sign In
+          </button>
+        </div>
 
-        <div className="mt-6 text-center text-sm text-muted-foreground">
-          <p>First user becomes administrator</p>
-          <p>Subsequent users require admin approval</p>
+        {/* Footer note */}
+        <div className="flex items-center gap-2 text-blue-300/40 text-xs">
+          <Shield className="h-3.5 w-3.5" />
+          <span>Authorized personnel only</span>
         </div>
       </div>
     </div>