fix: correct ISBN edge cases test expectation

- Fix "ISBN with multiple hyphens" test expected value
- Input "978-0-306-40615-7" should normalize to "9780306406157"

cmd/server/tests/media_item_isbn_test.go

@@ -258,7 +258,7 @@ func TestMediaItemISBNEdgeCases(t *testing.T) {
 		json.NewDecoder(resp.Body).Decode(&response)
 
 		assert.Equal(t, http.StatusCreated, resp.StatusCode)
-		assert.Equal(t, "9780123456789", response["isbn"])
+		assert.Equal(t, "9780306406157", response["isbn"])
 	})
 
 	t.Run("ISBN with trailing hyphen", func(t *testing.T) {