Alert on payment success or failure. (#1705)

## Description:

Alert on payment success or failure.

## 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 have read and accepted the CLA agreement (only required once).

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

evan

src/client/Cosmetics.ts

@@ -41,9 +41,8 @@ export async function handlePurchase(priceId: string) {
       },
       body: JSON.stringify({
         priceId: priceId,
-
-        successUrl: `${window.location.href}purchase-success`,
-        cancelUrl: `${window.location.href}purchase-cancel`,
+        successUrl: `${window.location.origin}#purchase-completed=true`,
+        cancelUrl: `${window.location.origin}#purchase-completed=false`,
       }),
     },
   );

src/client/Main.ts

@@ -423,8 +423,25 @@ class Client {
 
   private handleHash() {
     const { hash } = window.location;
+
+    const alertAndStrip = (message: string) => {
+      alert(message);
+      history.replaceState(
+        null,
+        "",
+        window.location.pathname + window.location.search,
+      );
+    };
+
     if (hash.startsWith("#")) {
       const params = new URLSearchParams(hash.slice(1));
+      if (params.get("purchase-completed") === "true") {
+        alertAndStrip("purchase succeeded");
+        return;
+      } else if (params.get("purchase-completed") === "false") {
+        alertAndStrip("purchase failed");
+        return;
+      }
       const lobbyId = params.get("join");
       if (lobbyId && ID.safeParse(lobbyId).success) {
         this.joinModal.open(lobbyId);