feat: Add real-time notification center with WebSocket integration

- Add in-app notification system with database storage
- Implement bell icon component with unread count badge in dashboard header
- Add full Notifications page tab with pagination and filtering (All/Unread/Read)
- Implement real-time WebSocket push notifications to all connected clients
- Add notification API endpoints: GET, PUT /read, DELETE, POST /clear
- Fix critical bug in notificationService where 'status' variable was undefined
- Add Notifications route to App.js routing
- Enhanced UI with notification popup in header and dedicated full-page view
- Auto-reconnect WebSocket with 5s timeout on disconnect
- Support rich notification content with resource details and timestamps

server/retryPolicy.js

@@ -0,0 +1,44 @@
+// Retry logic with exponential backoff
+class RetryPolicy {
+  constructor(maxRetries = 3, initialDelayMs = 1000, maxDelayMs = 10000) {
+    this.maxRetries = maxRetries;
+    this.initialDelayMs = initialDelayMs;
+    this.maxDelayMs = maxDelayMs;
+  }
+
+  async execute(fn, context = 'operation') {
+    let lastError;
+    
+    for (let attempt = 0; attempt <= this.maxRetries; attempt++) {
+      try {
+        return await fn();
+      } catch (error) {
+        lastError = error;
+        
+        if (attempt < this.maxRetries) {
+          const delay = this.calculateBackoff(attempt);
+          await this.sleep(delay);
+        }
+      }
+    }
+    
+    const error = new Error(`${context} failed after ${this.maxRetries + 1} attempts`);
+    error.originalError = lastError;
+    throw error;
+  }
+
+  calculateBackoff(attempt) {
+    // Exponential backoff: initialDelay * 2^attempt
+    // With jitter: ±10%
+    const exponentialDelay = this.initialDelayMs * Math.pow(2, attempt);
+    const cappedDelay = Math.min(exponentialDelay, this.maxDelayMs);
+    const jitter = cappedDelay * 0.1 * (Math.random() - 0.5);
+    return cappedDelay + jitter;
+  }
+
+  sleep(ms) {
+    return new Promise(resolve => setTimeout(resolve, ms));
+  }
+}
+
+module.exports = RetryPolicy;