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/social.py

@@ -0,0 +1,75 @@
+"""Social media models"""
+from sqlalchemy import Column, Integer, String, Text, Boolean, DateTime, ForeignKey
+from sqlalchemy.sql import func
+from app.database import Base
+
+
+class Post(Base):
+    """Social media post model"""
+
+    __tablename__ = "posts"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    content = Column(Text, nullable=False)
+    image_url = Column(String(500))
+    video_url = Column(String(500))
+
+    # Engagement metrics
+    likes_count = Column(Integer, default=0)
+    comments_count = Column(Integer, default=0)
+    shares_count = Column(Integer, default=0)
+    views_count = Column(Integer, default=0)
+
+    # Visibility
+    is_public = Column(Boolean, default=True)
+    is_pinned = Column(Boolean, default=False)
+
+    # Timestamps
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+    def __repr__(self):
+        return f"<Post {self.id}>"
+
+
+class Comment(Base):
+    """Comment model"""
+
+    __tablename__ = "comments"
+
+    id = Column(Integer, primary_key=True, index=True)
+    post_id = Column(Integer, ForeignKey("posts.id", ondelete="CASCADE"), nullable=False)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    content = Column(Text, nullable=False)
+    parent_id = Column(Integer, ForeignKey("comments.id", ondelete="CASCADE"))  # For nested comments
+
+    likes_count = Column(Integer, default=0)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+
+class Like(Base):
+    """Like model"""
+
+    __tablename__ = "likes"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    post_id = Column(Integer, ForeignKey("posts.id", ondelete="CASCADE"))
+    comment_id = Column(Integer, ForeignKey("comments.id", ondelete="CASCADE"))
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+
+class Follow(Base):
+    """Follow relationship model"""
+
+    __tablename__ = "follows"
+
+    id = Column(Integer, primary_key=True, index=True)
+    follower_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    following_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+
+    created_at = Column(DateTime(timezone=True), server_default=func.now())