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/auth.py

@@ -0,0 +1,100 @@
+"""Authentication utilities"""
+from datetime import datetime, timedelta
+from typing import Optional
+from jose import JWTError, jwt
+from passlib.context import CryptContext
+from fastapi import Depends, HTTPException, status
+from fastapi.security import OAuth2PasswordBearer
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select
+
+from app.config import settings
+from app.database import get_db
+from app.models.user import User
+
+# Password hashing
+pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+# OAuth2 scheme
+oauth2_scheme = OAuth2PasswordBearer(tokenUrl="/api/auth/login")
+
+
+def verify_password(plain_password: str, hashed_password: str) -> bool:
+    """Verify a password against a hash"""
+    return pwd_context.verify(plain_password, hashed_password)
+
+
+def get_password_hash(password: str) -> str:
+    """Hash a password"""
+    return pwd_context.hash(password)
+
+
+def create_access_token(data: dict, expires_delta: Optional[timedelta] = None) -> str:
+    """Create a JWT access token"""
+    to_encode = data.copy()
+    if expires_delta:
+        expire = datetime.utcnow() + expires_delta
+    else:
+        expire = datetime.utcnow() + timedelta(minutes=settings.ACCESS_TOKEN_EXPIRE_MINUTES)
+
+    to_encode.update({"exp": expire, "type": "access"})
+    encoded_jwt = jwt.encode(to_encode, settings.SECRET_KEY, algorithm=settings.ALGORITHM)
+    return encoded_jwt
+
+
+def create_refresh_token(data: dict) -> str:
+    """Create a JWT refresh token"""
+    to_encode = data.copy()
+    expire = datetime.utcnow() + timedelta(days=settings.REFRESH_TOKEN_EXPIRE_DAYS)
+    to_encode.update({"exp": expire, "type": "refresh"})
+    encoded_jwt = jwt.encode(to_encode, settings.SECRET_KEY, algorithm=settings.ALGORITHM)
+    return encoded_jwt
+
+
+async def get_current_user(
+    token: str = Depends(oauth2_scheme),
+    db: AsyncSession = Depends(get_db)
+) -> User:
+    """Get the current authenticated user"""
+    credentials_exception = HTTPException(
+        status_code=status.HTTP_401_UNAUTHORIZED,
+        detail="Could not validate credentials",
+        headers={"WWW-Authenticate": "Bearer"},
+    )
+
+    try:
+        payload = jwt.decode(token, settings.SECRET_KEY, algorithms=[settings.ALGORITHM])
+        user_id: int = payload.get("user_id")
+        if user_id is None:
+            raise credentials_exception
+    except JWTError:
+        raise credentials_exception
+
+    result = await db.execute(select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+
+    if user is None:
+        raise credentials_exception
+
+    return user
+
+
+async def get_current_active_user(
+    current_user: User = Depends(get_current_user)
+) -> User:
+    """Get the current active user"""
+    if not current_user.is_active:
+        raise HTTPException(status_code=400, detail="Inactive user")
+    return current_user
+
+
+async def get_current_admin_user(
+    current_user: User = Depends(get_current_active_user)
+) -> User:
+    """Get the current admin user"""
+    if not current_user.is_admin:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Not enough permissions"
+        )
+    return current_user