Await LanguageClient start during VSCode extension activation

[Copilot]

VSCode e2e tests were failing in CI with "Client is not running" errors. This race condition occurred because the extension activation hook was returning before the LanguageClient finished initializing, allowing test commands to fire before the server was ready.

Extension Activation

• Added await to client.start() to block the activate resolution until the LSP client is fully initialized.

  client = new LanguageClient(
    "badjuju",
    "Bad Juju",
    serverOptions,
    clientOptions,
  );
- client.start();
+ await client.start();