Add comprehensive Discord provider design documentation

[csharpfritz]

Complete design specifications for Discord channel monitoring:

• Discord-Provider-Design.md: WebSocket Gateway API integration architecture
• Discord-Technical-Implementation.md: WebSocket services and bot authentication
• Discord-UI-Specification.md: Bot setup wizard and Discord ID helpers
• Discord-Configuration-Guide.md: End-user bot creation and setup guide
• Discord-Implementation-Roadmap.md: 5-week development timeline

Discord provider enables real-time channel monitoring for gaming streams, developer conferences, community events, and live audience engagement.

Features: WebSocket connections, bot authentication, Discord API v10 integration, comprehensive bot setup guidance, and real-time message processing.