Update Navbar and useModularNavigation to replace 'BarChart3' icon with 'Store'

- Modify Navbar.vue to import and utilize the 'Store' icon in place of 'BarChart3' for improved visual representation.
- Update useModularNavigation.ts to change the icon for the 'Market Dashboard' from 'BarChart3' to 'Store', ensuring consistency across the application.

src/composables/useModularNavigation.ts

@@ -74,7 +74,7 @@ export function useModularNavigation() {
       items.push({ 
         name: 'Market Dashboard', 
         href: '/market-dashboard', 
-        icon: 'BarChart3',
+        icon: 'Store',
         requiresAuth: true 
       })
     }
@@ -103,4 +103,4 @@ export function useModularNavigation() {
     userMenuItems,
     isModuleAvailable
   }
-}
+}