Fix client-side bundling by separating server and client exports

- Create dedicated /server export for server-side functions and plugin
- Main export now contains only types (client-safe)
- Remove problematic /steps export that exposed server functions
- Update README with correct import structure
- Fix tests to use /server export

This prevents server-side code from being bundled in client JavaScript,
eliminating the "require is not defined in ES module scope" runtime error.

Breaking change: workflowsPlugin must now be imported from '/server':
import { workflowsPlugin } from '@xtr-dev/payload-automation/server'

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/test/basic.test.ts

@@ -0,0 +1,14 @@
+import { describe, it, expect } from 'vitest'
+
+describe('PayloadCMS Automation Plugin', () => {
+  it('should export the plugin function from server export', async () => {
+    const { workflowsPlugin } = await import('../exports/server.js')
+    expect(workflowsPlugin).toBeDefined()
+    expect(typeof workflowsPlugin).toBe('function')
+  })
+
+  it('should have the correct package name', async () => {
+    // Basic test to ensure the plugin can be imported
+    expect(true).toBe(true)
+  })
+})