docs(websockets): add JWT connection authentication guide

[faizkhairi]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Docs

What is the current behavior?

The WebSockets Guards page documents @UseGuards() on @SubscribeMessage() handlers only. It does not explain how to authenticate clients during the initial Socket.IO handleConnection() handshake.

Related discussion: nestjs/nest#882

Issue Number: N/A

What is the new behavior?

Adds an Authenticating connections section to content/websockets/guards.md covering:

• Why connection-time auth differs from message-scoped guards
• Verifying a JWT from handshake.auth or the Authorization header
• Disconnecting invalid clients in handleConnection()
• Joining user-specific rooms after verification
• A matching socket.io-client example

Does this PR introduce a breaking change?

• No

Other information

Verified locally:

npm run docs-only

Result: docs generated successfully (includes updated websockets/guards page).

Examples follow existing @@filename / @@switch conventions used elsewhere in the docs repo.