Add graceful shutdown button and improve shutdown status display

- Add refresh/shutdown button next to status indicator that gracefully
  stops the process without cleaning my-storage
- Create /api/shutdown endpoint that triggers graceful shutdown via SIGTERM
- Update status indicator to show "Gracefully Cleaning...." when system
  is shutting down (instead of "Searching for peers...")
- Include isShuttingDown flag in /api/status endpoint response
- Use built-in ConfirmationModal for shutdown confirmation with warning styling

The shutdown button appears in the top-right corner next to the status
indicator and uses the existing confirmation modal system for user
confirmation before initiating shutdown.

includes/admin/admin-backend/routes/status.js

@@ -14,7 +14,8 @@ async function handleStatusRoutes(req, res) {
         isMaster: state.isMaster,
         isConnected: !!state.dnsPass,
         peersCount: state.connectedPeers.size,
-        pid: process.pid
+        pid: process.pid,
+        isShuttingDown: state.isShuttingDown || false
       };
       trackRequest('/api/status', true);
       res.writeHead(200, { 'Content-Type': 'application/json' });
@@ -28,6 +29,30 @@ async function handleStatusRoutes(req, res) {
     return true;
   }
 
+  if (method === 'POST' && urlPath === '/api/shutdown') {
+    try {
+      const { logInfo } = require('../../../infrastructure/logger');
+      
+      // Send success response before shutting down
+      res.writeHead(200, { 'Content-Type': 'application/json' });
+      res.end(JSON.stringify({
+        success: true,
+        message: 'Graceful shutdown initiated. Process will exit after cleanup completes.'
+      }));
+      
+      // Trigger graceful shutdown after sending response
+      setTimeout(() => {
+        logInfo('Admin', 'Initiating graceful shutdown (without cleaning storage)...');
+        process.emit('SIGTERM');
+      }, 500); // Small delay to ensure response is sent
+    } catch (err) {
+      const errorResponse = createErrorResponse(err, 500);
+      res.writeHead(errorResponse.statusCode, errorResponse.headers);
+      res.end(errorResponse.body);
+    }
+    return true;
+  }
+
   if (method === 'GET' && urlPath === '/api/health') {
     try {
       const query = url.parse(req.url, true).query;