feat: Add backend routes and styles for banner management

- Introduced `banners.ts` with CRUD operations for managing banners.
- Added `/banners/active` endpoint to fetch active banners.
- Secured admin-only routes for banner creation, update, and deletion.
- Created `Banner.css` for banner styling.

src/styles/components/Banner.css

@@ -0,0 +1,26 @@
+.banner-wrapper {
+  width: 100%;
+  background-color: var(--color-orange1);
+  padding: 1rem 0;
+}
+
+.banner {
+  max-width: var(--container-max-width);
+  margin: 0 auto;
+  padding: 0 var(--padding-horizontal);
+}
+
+.banner p {
+  color: #000;
+  font-size: var(--font-size-small-medium);
+  font-weight: 600;
+  margin: 0;
+  text-align: center;
+  line-height: 1.4;
+}
+
+@media (max-width: 768px) {
+  .banner p {
+    font-size: var(--font-size-small);
+  }
+}