refactor: consolidate blockchain explorer into single app and update backup ignore patterns

- Remove standalone explorer-web app (README, HTML, package files)
- Add /web endpoint to blockchain-explorer for web interface access
- Update .gitignore to exclude application backup archives (*.tar.gz, *.zip)
- Add backup documentation files to .gitignore (BACKUP_INDEX.md, README.md)
- Consolidate explorer functionality into main blockchain-explorer application

apps/exchange/models.py

@@ -0,0 +1,109 @@
+#!/usr/bin/env python3
+"""
+Database models for the AITBC Trade Exchange
+"""
+
+from datetime import datetime
+from typing import Optional
+from sqlalchemy import Column, Integer, String, Float, DateTime, Boolean, ForeignKey, Index
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import relationship
+
+Base = declarative_base()
+
+
+class User(Base):
+    """User account for trading"""
+    __tablename__ = "users"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    username = Column(String(50), unique=True, index=True, nullable=False)
+    email = Column(String(100), unique=True, index=True, nullable=False)
+    password_hash = Column(String(255), nullable=False)
+    bitcoin_address = Column(String(100), unique=True, nullable=False)
+    aitbc_address = Column(String(100), unique=True, nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow)
+    is_active = Column(Boolean, default=True)
+    
+    # Relationships
+    orders = relationship("Order", back_populates="user")
+    trades = relationship("Trade", back_populates="buyer")
+    
+    def __repr__(self):
+        return f"<User(username='{self.username}')>"
+
+
+class Order(Base):
+    """Trading order (buy or sell)"""
+    __tablename__ = "orders"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    order_type = Column(String(4), nullable=False)  # 'BUY' or 'SELL'
+    amount = Column(Float, nullable=False)  # Amount of AITBC
+    price = Column(Float, nullable=False)  # Price in BTC
+    total = Column(Float, nullable=False)  # Total in BTC (amount * price)
+    filled = Column(Float, default=0.0)  # Amount filled
+    remaining = Column(Float, nullable=False)  # Amount remaining to fill
+    status = Column(String(20), default='OPEN')  # OPEN, PARTIALLY_FILLED, FILLED, CANCELLED
+    created_at = Column(DateTime, default=datetime.utcnow)
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    
+    # Relationships
+    user = relationship("User", back_populates="orders")
+    trades = relationship("Trade", back_populates="order")
+    
+    __table_args__ = (
+        Index('idx_order_type_status', 'order_type', 'status'),
+        Index('idx_price_status', 'price', 'status'),
+    )
+    
+    def __repr__(self):
+        return f"<Order(type='{self.order_type}', amount={self.amount}, price={self.price})>"
+
+
+class Trade(Base):
+    """Completed trade record"""
+    __tablename__ = "trades"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    buyer_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    seller_id = Column(Integer, ForeignKey("users.id"), nullable=False)
+    order_id = Column(Integer, ForeignKey("orders.id"), nullable=False)
+    amount = Column(Float, nullable=False)  # Amount of AITBC traded
+    price = Column(Float, nullable=False)  # Trade price in BTC
+    total = Column(Float, nullable=False)  # Total value in BTC
+    trade_hash = Column(String(100), unique=True, nullable=False)  # Blockchain transaction hash
+    created_at = Column(DateTime, default=datetime.utcnow)
+    
+    # Relationships
+    buyer = relationship("User", back_populates="trades", foreign_keys=[buyer_id])
+    seller = relationship("User", foreign_keys=[seller_id])
+    order = relationship("Order", back_populates="trades")
+    
+    __table_args__ = (
+        Index('idx_created_at', 'created_at'),
+        Index('idx_price', 'price'),
+    )
+    
+    def __repr__(self):
+        return f"<Trade(amount={self.amount}, price={self.price}, total={self.total})>"
+
+
+class Balance(Base):
+    """User balance tracking"""
+    __tablename__ = "balances"
+    
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id"), unique=True, nullable=False)
+    btc_balance = Column(Float, default=0.0)
+    aitbc_balance = Column(Float, default=0.0)
+    btc_locked = Column(Float, default=0.0)  # Locked in open orders
+    aitbc_locked = Column(Float, default=0.0)  # Locked in open orders
+    updated_at = Column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)
+    
+    # Relationship
+    user = relationship("User")
+    
+    def __repr__(self):
+        return f"<Balance(btc={self.btc_balance}, aitbc={self.aitbc_balance})>"