lobby websocket instead of polling (#2727)

## Description:
Changes game lobbies into websockets instead of polling

## 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:

w.o.n

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: iamlewis <lewismmmm@gmail.com>

tests/client/LobbySocket.test.ts

@@ -0,0 +1,113 @@
+import { PublicLobbySocket } from "../../src/client/LobbySocket";
+
+class MockWebSocket extends EventTarget {
+  static instances: MockWebSocket[] = [];
+  static readonly OPEN = 1;
+  static readonly CLOSED = 3;
+
+  readonly url: string;
+  readyState = MockWebSocket.OPEN;
+
+  constructor(url: string) {
+    super();
+    this.url = url;
+    MockWebSocket.instances.push(this);
+  }
+
+  addEventListener(
+    type: string,
+    listener: EventListenerOrEventListenerObject,
+    options?: boolean | AddEventListenerOptions,
+  ): void {
+    super.addEventListener(type, listener, options);
+  }
+
+  close(code?: number, reason?: string) {
+    this.readyState = MockWebSocket.CLOSED;
+    this.dispatchEvent(new CloseEvent("close", { code, reason }));
+  }
+
+  send(_data: unknown) {}
+}
+
+describe("PublicLobbySocket", () => {
+  const originalWebSocket = globalThis.WebSocket;
+  const originalFetch = globalThis.fetch;
+
+  beforeEach(() => {
+    MockWebSocket.instances = [];
+    // @ts-expect-error assign test mock
+    globalThis.WebSocket = MockWebSocket;
+  });
+
+  afterEach(() => {
+    globalThis.WebSocket = originalWebSocket;
+    globalThis.fetch = originalFetch;
+    vi.useRealTimers();
+  });
+
+  it("delivers lobby updates from websocket messages", () => {
+    const updates: unknown[][] = [];
+    const socket = new PublicLobbySocket((lobbies) => updates.push(lobbies));
+
+    socket.start();
+    const ws = MockWebSocket.instances.at(-1);
+    expect(ws?.url).toContain("/lobbies");
+
+    ws?.dispatchEvent(
+      new MessageEvent("message", {
+        data: JSON.stringify({
+          type: "lobbies_update",
+          data: {
+            lobbies: [
+              {
+                gameID: "g1",
+                numClients: 1,
+                gameConfig: {
+                  maxPlayers: 2,
+                  gameMode: 0,
+                  gameMap: "Earth",
+                },
+              },
+            ],
+          },
+        }),
+      }),
+    );
+
+    expect(updates).toHaveLength(1);
+    expect((updates[0][0] as { gameID: string }).gameID).toBe("g1");
+
+    socket.stop();
+  });
+
+  it("falls back to HTTP polling after max websocket attempts", async () => {
+    vi.useFakeTimers();
+
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ lobbies: [] }),
+    });
+
+    globalThis.fetch = fetchMock as unknown as typeof fetch;
+
+    const socket = new PublicLobbySocket(() => {}, {
+      maxWsAttempts: 1,
+      reconnectDelay: 0,
+      pollIntervalMs: 50,
+    });
+
+    socket.start();
+    const ws = MockWebSocket.instances.at(-1);
+    ws?.dispatchEvent(new CloseEvent("close"));
+
+    await Promise.resolve();
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+
+    vi.advanceTimersByTime(60);
+    await Promise.resolve();
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+
+    socket.stop();
+  });
+});