feat: implement GET /items/{id} endpoint

- Add UUID parsing with error handling for malformed IDs
- Search library using SearchCriteria with ID filter
- Return 404 for non-existent items, 200 for found items
- Return 400 for invalid UUID format

Author: lquinoa252

lesson_23/api/java/api_app/src/main/java/com/codedifferently/lesson23/web/MediaItemsController.java

@@ -7,9 +7,11 @@
 import java.io.IOException;
 import java.util.List;
 import java.util.Set;
+import java.util.UUID;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.CrossOrigin;
 import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RestController;
 
 @RestController
@@ -31,4 +33,22 @@ public ResponseEntity<GetMediaItemsResponse> getItems() {
     var response = GetMediaItemsResponse.builder().items(responseItems).build();
     return ResponseEntity.ok(response);
   }
+
+  @GetMapping("/items/{id}")
+  public ResponseEntity<MediaItemResponse> getItem(@PathVariable String id) {
+    try {
+      UUID itemId = UUID.fromString(id);
+      Set<MediaItem> items = library.search(SearchCriteria.builder().id(itemId.toString()).build());
+      
+      if (items.isEmpty()) {
+        return ResponseEntity.notFound().build();
+      }
+      
+      MediaItem item = items.iterator().next();
+      MediaItemResponse response = MediaItemResponse.from(item);
+      return ResponseEntity.ok(response);
+    } catch (IllegalArgumentException e) {
+      return ResponseEntity.badRequest().build();
+    }
+  }
 }