Export workflow generates .env.example with all plugin env vars instead of only required ones

[BowTiedSwan]

When exporting a workflow as code, the generated .env.example includes environment variables for all registered integrations, not just the ones used in the workflow.

Steps to reproduce:

1. Create a workflow with a single Resend action
2. Click "Export Workflow as Code"
3. Open the generated .env.example

Expected: Only RESEND_API_KEY is listed Actual: Env vars for Stripe, GitHub, Linear, Slack, and all other plugins are included This makes it unclear which credentials are actually needed to run the exported project.

[BowTiedSwan]

Opened a PR to this this: #172