Rewarded videos ads to test a skin (#3120)

## Description:

Added rewarded video ads for skin trials via Playwire's
manuallyCreateRewardUi API. Users can now click "Try me" to watch a
video ad and receive a temporary skin trial. Upon completion a temporary
flare is granted to the player so they have ~5 minutes to use the skin.

added getPlayerCosmeticsRefs and getPlayerCosmetics to Cosmetics.ts to
centralize cosmetic retrieval & validation.

<img width="801" height="534" alt="Screenshot 2026-02-10 at 7 58 14 PM"
src="https://github.com/user-attachments/assets/51cc378c-2feb-4692-8cf2-20ee54cea3b8"
/>

## 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

src/core/game/UserSettings.ts

@@ -192,6 +192,12 @@ export class UserSettings {
     }
   }
 
+  getFlag(): string | undefined {
+    const flag = localStorage.getItem("flag");
+    if (!flag || flag === "xx") return undefined;
+    return flag;
+  }
+
   backgroundMusicVolume(): number {
     return this.getFloat("settings.backgroundMusicVolume", 0);
   }