add openfront copyright to loading screen (#2151)

## Description:

This will make the copyright notice more clear.


<img width="369" height="242" alt="Screenshot 2025-10-07 at 6 03 44 PM"
src="https://github.com/user-attachments/assets/53925a24-bf1a-437e-84c1-3d146d598bfd"
/>

## 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

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

evan

resources/lang/en.json

@@ -249,6 +249,7 @@
   },
   "game_starting_modal": {
     "title": "Game is Starting...",
+    "code_license": "Code licensed under AGPL-3.0",
     "desc": "Preparing for the lobby to start. Please wait."
   },
   "difficulty": {