feat(auth): polish login/register with logo, gradients and animations

frontend/src/pages/LoginPage.jsx

@@ -1,6 +1,7 @@
 import { useState } from 'react';
 import { useNavigate, Link } from 'react-router-dom';
 import { useAuth } from '../context/AuthContext';
+import Logo from '../components/Logo';
 
 export default function LoginPage() {
   const [email, setEmail] = useState('');
@@ -26,9 +27,10 @@ export default function LoginPage() {
   return (
     <div className="auth-page">
       <div className="auth-card">
-        <h1>🏋️ Gravl</h1>
-        <h2>Logga in</h2>
-        {error && <div className="error">{error}</div>}
+        <Logo />
+        <h1 className="auth-title">Logga in</h1>
+        <p className="auth-tagline">Din personliga träningspartner</p>
+        {error && <div className="error auth-error">{error}</div>}
         <form onSubmit={handleSubmit}>
           <input type="email" placeholder="E-post" value={email} onChange={e => setEmail(e.target.value)} required />
           <input type="password" placeholder="Lösenord" value={password} onChange={e => setPassword(e.target.value)} required />

frontend/src/pages/RegisterPage.jsx

@@ -1,6 +1,7 @@
 import { useState } from 'react';
 import { useNavigate, Link } from 'react-router-dom';
 import { useAuth } from '../context/AuthContext';
+import Logo from '../components/Logo';
 
 export default function RegisterPage() {
   const [email, setEmail] = useState('');
@@ -26,9 +27,10 @@ export default function RegisterPage() {
   return (
     <div className="auth-page">
       <div className="auth-card">
-        <h1>🏋️ Gravl</h1>
-        <h2>Skapa konto</h2>
-        {error && <div className="error">{error}</div>}
+        <Logo />
+        <h1 className="auth-title">Skapa konto</h1>
+        <p className="auth-tagline">Börja din träningsresa</p>
+        {error && <div className="error auth-error">{error}</div>}
         <form onSubmit={handleSubmit}>
           <input type="email" placeholder="E-post" value={email} onChange={e => setEmail(e.target.value)} required />
           <input type="password" placeholder="Lösenord" value={password} onChange={e => setPassword(e.target.value)} required minLength={6} />