Make SpawnAd loading text translatable using translateText (#1393)

## Description:
Replaced the hardcoded "loading" text in the SpawnAd component with
`translateText("spawn_ad.loading")` for proper localization.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

## Please put your Discord username so you can be contacted if a bug or
regression is found:

aotumuri

resources/lang/en.json

@@ -576,6 +576,9 @@
       "grogu": "Grogu"
     }
   },
+  "spawn_ad": {
+    "loading": "Loading advertisement..."
+  },
   "auth": {
     "login_required": "Login is required to access this website.",
     "redirecting": "You are being redirected...",