Fix forbidClientAccountCreation Documentation Issue

Problem

Users were confused when setting forbidClientAccountCreation: true in Accounts.config() only on the server side. While this successfully blocks account creation calls, the accounts-ui package still shows the "Create account" link because it only checks the client-side configuration.

Solution

Updated the JSDoc documentation for Accounts.config() to clearly explain:

1. Added warning to forbidClientAccountCreation parameter explaining it must be set on both client and server
2. Added practical example showing how to create a shared configuration file that can be imported on both sides
3. Explains the behavior when only set on server (creation blocked but UI link still visible)

Changes Made

• Enhanced JSDoc documentation in packages/accounts-base/accounts_common.js
• Added clear warning with Important notation
• Included code example showing best practice approach

Example Usage

// lib/accounts-config.js (shared)
import { Accounts } from 'meteor/accounts-base';

Accounts.config({
  forbidClientAccountCreation: true,
  sendVerificationEmail: true,
});

// Import in both client/main.js and server/main.js
import '../lib/accounts-config.js';

Verification

• No breaking changes to existing functionality
• Documentation is clear and actionable
• Follows existing JSDoc patterns in the codebase

Fixes #13922