Enhance architecture documentation with colorful Mermaid diagrams

Add comprehensive architecture documentation to README

Clean up repository and update README for streaming focus

Fix datetime serialization issue in streaming

Fix streaming endpoints with working implementation

Add high-throughput streaming endpoints for 10K+ messages/sec

Fix Railway deployment issues

Add Railway Kafka integration with security configuration

Update Railway deployment link with correct repository URL

Add Railway deployment button and deployment instructions

Initial commit: Complete FastAPI clickstream data generator