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/app/models/blockchain.py

@@ -0,0 +1,94 @@
+"""Blockchain and cryptocurrency models"""
+from sqlalchemy import Column, Integer, String, Text, DateTime, ForeignKey, Float, Boolean
+from sqlalchemy.sql import func
+from app.database import Base
+
+
+class Wallet(Base):
+    """Cryptocurrency wallet model"""
+
+    __tablename__ = "wallets"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+
+    address = Column(String(255), unique=True, nullable=False, index=True)
+    private_key = Column(String(500), nullable=False)  # Encrypted
+    public_key = Column(String(500), nullable=False)
+
+    balance = Column(Float, default=0.0)
+
+    # Metadata
+    label = Column(String(100))
+    is_primary = Column(Boolean, default=True)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+
+class Transaction(Base):
+    """Blockchain transaction model"""
+
+    __tablename__ = "transactions"
+
+    id = Column(Integer, primary_key=True, index=True)
+
+    # Transaction details
+    transaction_hash = Column(String(255), unique=True, nullable=False, index=True)
+    from_address = Column(String(255), nullable=False, index=True)
+    to_address = Column(String(255), nullable=False, index=True)
+    amount = Column(Float, nullable=False)
+    fee = Column(Float, default=0.0)
+
+    # Block information
+    block_id = Column(Integer, ForeignKey("blocks.id", ondelete="SET NULL"))
+    block_index = Column(Integer)
+
+    # Status
+    is_confirmed = Column(Boolean, default=False)
+    confirmations = Column(Integer, default=0)
+
+    # Metadata
+    signature = Column(Text, nullable=False)
+    message = Column(Text)  # Optional transaction message
+
+    # Timestamps
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    confirmed_at = Column(DateTime(timezone=True))
+
+    def __repr__(self):
+        return f"<Transaction {self.transaction_hash}>"
+
+
+class Block(Base):
+    """Blockchain block model"""
+
+    __tablename__ = "blocks"
+
+    id = Column(Integer, primary_key=True, index=True)
+
+    # Block data
+    index = Column(Integer, unique=True, nullable=False, index=True)
+    timestamp = Column(DateTime(timezone=True), nullable=False)
+    nonce = Column(Integer, nullable=False)
+    previous_hash = Column(String(255), nullable=False)
+    hash = Column(String(255), unique=True, nullable=False, index=True)
+    merkle_root = Column(String(255))
+
+    # Mining
+    miner_id = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"))
+    miner_address = Column(String(255))
+    difficulty = Column(Integer, nullable=False)
+    reward = Column(Float, default=0.0)
+
+    # Block metadata
+    transaction_count = Column(Integer, default=0)
+    size = Column(Integer)  # in bytes
+
+    # Validation
+    is_valid = Column(Boolean, default=True)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+    def __repr__(self):
+        return f"<Block {self.index}>"