fix private game join link (#1997)

## Description:

Main.ts wasn't handling the join properly.

## 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/client/Main.ts

@@ -476,8 +476,8 @@ class Client {
       return;
     }
 
-    if (decodedHash.startsWith("#join")) {
-      const lobbyId = params.get("lobby");
+    if (decodedHash.startsWith("#join=")) {
+      const lobbyId = decodedHash.substring(6); // Remove "#join="
       if (lobbyId && ID.safeParse(lobbyId).success) {
         this.joinModal.open(lobbyId);
         console.log(`joining lobby ${lobbyId}`);