Move blockchain app READMEs to centralized documentation

- Relocate blockchain-event-bridge README content to docs/apps/blockchain/blockchain-event-bridge.md
- Relocate blockchain-explorer README content to docs/apps/blockchain/blockchain-explorer.md
- Replace app READMEs with redirect notices pointing to new documentation location
- Consolidate documentation in central docs/ directory for better organization

docs/apps/exchange/trading-engine.md

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+# Trading Engine
+
+## Status
+✅ Operational
+
+## Overview
+High-performance trading engine for order matching, execution, and trade settlement with support for multiple order types and trading strategies.
+
+## Architecture
+
+### Core Components
+- **Order Matching Engine**: Real-time order matching algorithm
+- **Trade Executor**: Executes matched trades
+- **Risk Manager**: Risk assessment and position management
+- **Settlement Engine**: Trade settlement and clearing
+- **Order Book Manager**: Manages order book state
+- **Price Engine**: Calculates fair market prices
+
+## Quick Start (End Users)
+
+### Prerequisites
+- Python 3.13+
+- PostgreSQL database
+- Redis for caching
+- Access to exchange APIs
+
+### Installation
+```bash
+cd /opt/aitbc/apps/trading-engine
+.venv/bin/pip install -r requirements.txt
+```
+
+### Configuration
+Set environment variables in `.env`:
+```bash
+DATABASE_URL=postgresql://user:pass@localhost/trading
+REDIS_URL=redis://localhost:6379
+EXCHANGE_API_KEY=your-api-key
+RISK_LIMITS_ENABLED=true
+```
+
+### Running the Service
+```bash
+.venv/bin/python main.py
+```
+
+## Developer Guide
+
+### Development Setup
+1. Clone the repository
+2. Create virtual environment: `python -m venv .venv`
+3. Install dependencies: `pip install -r requirements.txt`
+4. Set up database
+5. Configure environment variables
+6. Run tests: `pytest tests/`
+
+### Project Structure
+```
+trading-engine/
+├── src/
+│   ├── matching_engine/      # Order matching logic
+│   ├── trade_executor/       # Trade execution
+│   ├── risk_manager/         # Risk management
+│   ├── settlement_engine/    # Trade settlement
+│   ├── order_book/           # Order book management
+│   └── price_engine/         # Price calculation
+├── tests/                    # Test suite
+└── pyproject.toml            # Project configuration
+```
+
+### Testing
+```bash
+# Run all tests
+pytest tests/
+
+# Run matching engine tests
+pytest tests/test_matching.py
+
+# Run risk manager tests
+pytest tests/test_risk.py
+```
+
+## API Reference
+
+### Order Management
+
+#### Submit Order
+```http
+POST /api/v1/trading/orders
+Content-Type: application/json
+
+{
+  "user_id": "string",
+  "symbol": "BTC_AIT",
+  "side": "buy|sell",
+  "type": "limit|market|stop",
+  "quantity": 100,
+  "price": 1.0,
+  "stop_price": 1.1
+}
+```
+
+#### Cancel Order
+```http
+DELETE /api/v1/trading/orders/{order_id}
+```
+
+#### Get Order Status
+```http
+GET /api/v1/trading/orders/{order_id}
+```
+
+### Trade Execution
+
+#### Get Trade History
+```http
+GET /api/v1/trading/trades?symbol=BTC_AIT&limit=100
+```
+
+#### Get User Trades
+```http
+GET /api/v1/trading/users/{user_id}/trades
+```
+
+### Risk Management
+
+#### Check Risk Limits
+```http
+POST /api/v1/trading/risk/check
+Content-Type: application/json
+
+{
+  "user_id": "string",
+  "order": {}
+}
+```
+
+#### Get User Risk Profile
+```http
+GET /api/v1/trading/users/{user_id}/risk-profile
+```
+
+### Settlement
+
+#### Get Settlement Status
+```http
+GET /api/v1/trading/settlement/{trade_id}
+```
+
+#### Trigger Settlement
+```http
+POST /api/v1/trading/settlement/trigger
+Content-Type: application/json
+
+{
+  "trade_ids": ["trade1", "trade2"]
+}
+```
+
+## Configuration
+
+### Environment Variables
+- `DATABASE_URL`: PostgreSQL connection string
+- `REDIS_URL`: Redis connection string
+- `EXCHANGE_API_KEY`: Exchange API key
+- `RISK_LIMITS_ENABLED`: Enable risk management
+- `MAX_POSITION_SIZE`: Maximum position size
+- `MARGIN_REQUIREMENT`: Margin requirement percentage
+- `LIQUIDATION_THRESHOLD`: Liquidation threshold
+
+### Order Types
+- **Limit Order**: Execute at specified price or better
+- **Market Order**: Execute immediately at market price
+- **Stop Order**: Trigger when price reaches stop price
+- **Stop-Limit**: Limit order triggered by stop price
+
+### Risk Parameters
+- **Position Limits**: Maximum position sizes
+- **Margin Requirements**: Required margin for leverage
+- **Liquidation Threshold**: Price at which positions are liquidated
+
+## Troubleshooting
+
+**Order not matched**: Check order book depth and price settings.
+
+**Trade execution failed**: Verify exchange connectivity and balance.
+
+**Risk check failed**: Review user risk profile and position limits.
+
+**Settlement delayed**: Check blockchain network status and gas fees.
+
+## Security Notes
+
+- Implement order validation
+- Use rate limiting for order submission
+- Monitor for wash trading
+- Validate user authentication
+- Implement position limits
+- Regularly audit trade history