Mock sample: Discord API

[waldekmastykarz]

Description

Create a mock sample for the Discord API.

Why

• Massive developer community building bots and integrations
• Gateway events and webhook testing is complex
• Slash commands and interactions require careful testing
• Enables bot development without live server

Suggested endpoints to mock

• REST API (messages, channels, guilds, users)
• Interactions (slash commands, buttons, select menus)
• Webhook delivery
• Rate limiting responses
• Gateway event simulation