Mock sample: SendGrid API

[waldekmastykarz]

Description

Create a mock sample for the SendGrid email API.

Why

• One of the most popular email delivery APIs
• Larger market share than Postmark/Resend
• Testing email delivery without actually sending emails
• Webhook simulation for delivery/bounce/open events

Suggested endpoints to mock

• Mail send endpoint
• Email validation
• Delivery webhooks (delivered, bounced, opened, clicked)
• Suppression list management
• Template rendering