fix: prevent sendStartGameMsg from crashing server on client disconnect (#3939)

The catch block in sendStartGameMsg() re-throws the error, which means a
single client's WebSocket failure (e.g. disconnected during game start)
propagates up and can crash the entire game server. The start() method
calls sendStartGameMsg() in a forEach loop over all clients, so one bad
client kills the game for everyone.

Changes:
- Added readyState check before sending
- Replaced re-throw with structured error logging
- A single client failure now logs the error and continues gracefully

If this PR fixes an issue, link it below. If not, delete these two
lines.
Resolves #(issue number)

## Description:

Describe the PR.

## Please complete the following:

- [ ] I have added screenshots for all UI updates
- [ ] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [ ] I have added relevant tests to the test directory
- [ ] 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:

DISCORD_USERNAME

src/server/GameServer.ts

@@ -783,6 +783,13 @@ export class GameServer {
     });
 
     try {
+      if (ws.readyState !== WebSocket.OPEN) {
+        this.log.warn(`WebSocket not open, skipping start message`, {
+          clientID: client.clientID,
+          readyState: ws.readyState,
+        });
+        return;
+      }
       ws.send(
         JSON.stringify({
           type: "start",
@@ -793,14 +800,10 @@ export class GameServer {
         } satisfies ServerStartGameMessage),
       );
     } catch (error) {
-      // can be enabled once we can use {cause: error} in Error constructor starting with ES2022
-      // eslint-disable-next-line preserve-caught-error
-      throw new Error(
-        `error sending start message for game ${this.id}, ${error}`.substring(
-          0,
-          250,
-        ),
-      );
+      this.log.error(`error sending start message for game ${this.id}`, {
+        clientID: client.clientID,
+        error: error instanceof Error ? error.message : String(error),
+      });
     }
   }