Add comprehensive session security to admin panel

Security improvements:
- Auto-logout after 30 minutes of inactivity
- Session warning 5 minutes before expiry with option to extend
- Activity-based session extension on user interaction
- Session validation on page load and API calls
- Periodic session validity checks every minute
- Secure cleanup of tokens and timers on logout
- Protection against expired session usage

This prevents unauthorized access if admin leaves session open or if tokens are compromised.

public/admin.js

@@ -2,6 +2,12 @@ document.addEventListener('DOMContentLoaded', () => {
     let authToken = localStorage.getItem('adminToken');
     let allLocations = [];
     let editingRowId = null;
+    let sessionTimeout = null;
+    let warningTimeout = null;
+    
+    // Session timeout settings (in milliseconds)
+    const SESSION_DURATION = 30 * 60 * 1000; // 30 minutes
+    const WARNING_TIME = 5 * 60 * 1000; // Show warning 5 minutes before expiry
 
     const loginSection = document.getElementById('login-section');
     const adminSection = document.getElementById('admin-section');
@@ -11,10 +17,19 @@ document.addEventListener('DOMContentLoaded', () => {
     const refreshBtn = document.getElementById('refresh-btn');
     const locationsTableBody = document.getElementById('locations-tbody');
 
-    // Check if already logged in
+    // Check if already logged in and session is still valid
     if (authToken) {
-        showAdminSection();
-        loadLocations();
+        const loginTime = localStorage.getItem('adminLoginTime');
+        const now = Date.now();
+        
+        if (loginTime && (now - parseInt(loginTime)) < SESSION_DURATION) {
+            showAdminSection();
+            loadLocations();
+            startSessionTimer();
+        } else {
+            // Session expired
+            logout('Session expired. Please log in again.');
+        }
     }
 
     // Login form handler
@@ -34,8 +49,10 @@ document.addEventListener('DOMContentLoaded', () => {
             if (response.ok) {
                 authToken = data.token;
                 localStorage.setItem('adminToken', authToken);
+                localStorage.setItem('adminLoginTime', Date.now().toString());
                 showAdminSection();
                 loadLocations();
+                startSessionTimer();
             } else {
                 showMessage(loginMessage, data.error, 'error');
             }
@@ -46,9 +63,7 @@ document.addEventListener('DOMContentLoaded', () => {
 
     // Logout handler
     logoutBtn.addEventListener('click', () => {
-        authToken = null;
-        localStorage.removeItem('adminToken');
-        showLoginSection();
+        logout('Logged out successfully.');
     });
 
     // Refresh button handler
@@ -78,6 +93,101 @@ document.addEventListener('DOMContentLoaded', () => {
     function hideMessage(element) {
         element.style.display = 'none';
     }
+    
+    // Session management functions
+    function startSessionTimer() {
+        clearSessionTimers();
+        
+        // Set warning timer (5 minutes before expiry)
+        warningTimeout = setTimeout(() => {
+            showSessionWarning();
+        }, SESSION_DURATION - WARNING_TIME);
+        
+        // Set logout timer (30 minutes)
+        sessionTimeout = setTimeout(() => {
+            logout('Session expired due to inactivity.');
+        }, SESSION_DURATION);
+    }
+    
+    function clearSessionTimers() {
+        if (sessionTimeout) {
+            clearTimeout(sessionTimeout);
+            sessionTimeout = null;
+        }
+        if (warningTimeout) {
+            clearTimeout(warningTimeout);
+            warningTimeout = null;
+        }
+    }
+    
+    function showSessionWarning() {
+        const extend = confirm('Your admin session will expire in 5 minutes. Click OK to extend your session, or Cancel to log out now.');
+        if (extend) {
+            extendSession();
+        } else {
+            logout('Session ended by user.');
+        }
+    }
+    
+    function extendSession() {
+        // Update login time and restart timers
+        localStorage.setItem('adminLoginTime', Date.now().toString());
+        startSessionTimer();
+        console.log('Admin session extended for 30 minutes');
+    }
+    
+    function logout(message = 'Logged out.') {
+        clearSessionTimers();
+        authToken = null;
+        localStorage.removeItem('adminToken');
+        localStorage.removeItem('adminLoginTime');
+        showLoginSection();
+        if (message) {
+            showMessage(loginMessage, message, 'error');
+        }
+    }
+    
+    // Reset session timer on user activity
+    function resetSessionTimer() {
+        if (authToken && adminSection.style.display !== 'none') {
+            const loginTime = localStorage.getItem('adminLoginTime');
+            const now = Date.now();
+            
+            // Only reset if we're within the session duration
+            if (loginTime && (now - parseInt(loginTime)) < SESSION_DURATION) {
+                localStorage.setItem('adminLoginTime', now.toString());
+                startSessionTimer();
+            }
+        }
+    }
+    
+    // Listen for user activity to reset session timer
+    const activityEvents = ['mousedown', 'mousemove', 'keypress', 'scroll', 'touchstart', 'click'];
+    let activityTimer = null;
+    
+    activityEvents.forEach(event => {
+        document.addEventListener(event, () => {
+            // Throttle activity detection to once per minute
+            if (!activityTimer) {
+                activityTimer = setTimeout(() => {
+                    resetSessionTimer();
+                    activityTimer = null;
+                }, 60000); // 1 minute throttle
+            }
+        }, true);
+    });
+    
+    // Check session validity periodically
+    setInterval(() => {
+        if (authToken) {
+            const loginTime = localStorage.getItem('adminLoginTime');
+            const now = Date.now();
+            
+            if (!loginTime || (now - parseInt(loginTime)) >= SESSION_DURATION) {
+                logout('Session expired.');
+            }
+        }
+    }, 60000); // Check every minute
 
     async function loadLocations() {
         try {
@@ -87,9 +197,7 @@ document.addEventListener('DOMContentLoaded', () => {
 
             if (response.status === 401) {
                 // Token expired or invalid
-                authToken = null;
-                localStorage.removeItem('adminToken');
-                showLoginSection();
+                logout('Session expired. Please log in again.');
                 return;
             }