Add logout function and ADMIN_PASSWORD environment validation

app/admin/page.tsx

@@ -151,6 +151,17 @@ export default function AdminPage() {
         }
     };
 
+    const handleLogout = () => {
+        localStorage.removeItem('hoerdle_admin_auth');
+        setIsAuthenticated(false);
+        setPassword('');
+        // Reset all state
+        setSongs([]);
+        setGenres([]);
+        setSpecials([]);
+        setDailyPuzzles([]);
+    };
+
     // Helper function to add auth headers to requests
     const getAuthHeaders = () => {
         const authToken = localStorage.getItem('hoerdle_admin_auth');
@@ -779,7 +790,24 @@ export default function AdminPage() {
 
     return (
         <div className="admin-container">
-            <h1 className="title" style={{ marginBottom: '2rem' }}>Hördle Admin Dashboard</h1>
+            <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: '2rem' }}>
+                <h1 className="title" style={{ margin: 0 }}>Hördle Admin Dashboard</h1>
+                <button
+                    onClick={handleLogout}
+                    className="btn-secondary"
+                    style={{
+                        padding: '0.5rem 1rem',
+                        backgroundColor: '#dc3545',
+                        color: 'white',
+                        border: 'none',
+                        borderRadius: '4px',
+                        cursor: 'pointer',
+                        fontSize: '0.9rem'
+                    }}
+                >
+                    🚪 Logout
+                </button>
+            </div>
 
             {/* Special Management */}
             <div className="admin-card" style={{ marginBottom: '2rem' }}>