add changes

frontend/src/app/shared/components/sidebar/sidebar.html

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+<aside class="sidebar" [class.open]="isOpen()">
+  <nav class="sidebar-nav">
+    <mat-nav-list>
+      @for (item of navItems; track item.route) {
+        @if (shouldShowItem(item)) {
+          <a 
+            mat-list-item 
+            [routerLink]="item.route"
+            [class.active]="isActiveRoute(item.route)"
+            [matTooltip]="item.label"
+            matTooltipPosition="right"
+            [matTooltipDisabled]="isOpen()">
+            <mat-icon matListItemIcon [matBadge]="item.badge" matBadgeColor="accent">
+              {{ item.icon }}
+            </mat-icon>
+            <span matListItemTitle class="nav-label">{{ item.label }}</span>
+          </a>
+          
+          @if (item.dividerAfter) {
+            <mat-divider></mat-divider>
+          }
+        }
+      }
+    </mat-nav-list>
+    
+    <!-- Guest Mode Section -->
+    @if (!isAuthenticated) {
+      <div class="guest-section">
+        <mat-divider></mat-divider>
+        <div class="guest-prompt">
+          <mat-icon>info</mat-icon>
+          <p>Sign up for full access</p>
+          <button mat-raised-button color="primary" routerLink="/register">
+            Create Account
+          </button>
+        </div>
+      </div>
+    }
+  </nav>
+</aside>