Add comprehensive FastAPI backend for BlackRoad OS

This commit adds a complete backend infrastructure with:

**Core Infrastructure:**
- FastAPI application with async/await support
- PostgreSQL database with SQLAlchemy ORM
- Redis caching layer
- JWT authentication and authorization
- Docker and Docker Compose configuration

**API Services:**
- Authentication API (register, login, JWT tokens)
- RoadMail API (email service with folders, send/receive)
- BlackRoad Social API (posts, comments, likes, follows)
- BlackStream API (video streaming with views/likes)
- File Storage API (file explorer with upload/download)
- RoadCoin Blockchain API (mining, transactions, wallet)
- AI Chat API (conversations with AI assistant)

**Database Models:**
- User accounts with wallet integration
- Email and folder management
- Social media posts and engagement
- Video metadata and analytics
- File storage with sharing
- Blockchain blocks and transactions
- AI conversation history

**Features:**
- Complete CRUD operations for all services
- Real-time blockchain mining with proof-of-work
- Transaction validation and wallet management
- File upload with S3 integration (ready)
- Social feed with engagement metrics
- Email system with threading support
- AI chat with conversation persistence

**Documentation:**
- Comprehensive README with setup instructions
- API documentation (Swagger/ReDoc auto-generated)
- Deployment guide for multiple platforms
- Testing framework with pytest

**DevOps:**
- Docker containerization
- Docker Compose for local development
- Database migrations with Alembic
- Health check endpoints
- Makefile for common tasks

All APIs are production-ready with proper error handling,
input validation, and security measures.

backend/.env.example

@@ -0,0 +1,41 @@
+# Database
+DATABASE_URL=postgresql://blackroad:password@localhost:5432/blackroad_db
+DATABASE_ASYNC_URL=postgresql+asyncpg://blackroad:password@localhost:5432/blackroad_db
+
+# Redis
+REDIS_URL=redis://localhost:6379/0
+
+# JWT
+SECRET_KEY=your-secret-key-change-this-in-production
+ALGORITHM=HS256
+ACCESS_TOKEN_EXPIRE_MINUTES=30
+REFRESH_TOKEN_EXPIRE_DAYS=7
+
+# AWS S3 (for file storage)
+AWS_ACCESS_KEY_ID=your-access-key
+AWS_SECRET_ACCESS_KEY=your-secret-key
+AWS_REGION=us-east-1
+S3_BUCKET_NAME=blackroad-files
+
+# Email (SMTP)
+SMTP_HOST=smtp.gmail.com
+SMTP_PORT=587
+SMTP_USER=your-email@gmail.com
+SMTP_PASSWORD=your-app-password
+EMAIL_FROM=noreply@blackroad.com
+
+# Application
+APP_NAME=BlackRoad Operating System
+APP_VERSION=1.0.0
+DEBUG=True
+ENVIRONMENT=development
+
+# CORS
+ALLOWED_ORIGINS=http://localhost:3000,http://localhost:8000,https://blackboxprogramming.github.io
+
+# API Keys
+OPENAI_API_KEY=your-openai-key-for-ai-chat
+
+# Blockchain
+BLOCKCHAIN_DIFFICULTY=4
+MINING_REWARD=50