Add FastAPI backend for energy trading system

Implements FastAPI backend with ML model support for energy trading,
including price prediction models and RL-based battery trading policy.
Features dashboard, trading, backtest, and settings API routes with
WebSocket support for real-time updates.

backend/README.md

@@ -0,0 +1,54 @@
+# Energy Trading Backend
+
+FastAPI backend for the energy trading system with ML model support.
+
+## Setup
+
+```bash
+cd backend
+pip install -r requirements.txt
+cp .env.example .env
+```
+
+## Running
+
+```bash
+uvicorn app.main:app --reload --host 0.0.0.0 --port 8000
+```
+
+## API Documentation
+
+- Swagger UI: http://localhost:8000/docs
+- ReDoc: http://localhost:8000/redoc
+
+## Project Structure
+
+```
+backend/
+├── app/
+│   ├── api/              # API routes and WebSocket
+│   ├── services/         # Business logic services
+│   ├── tasks/            # Background tasks
+│   ├── ml/               # ML models and training
+│   ├── models/           # Pydantic models
+│   └── utils/            # Utilities
+├── models/               # Trained models
+├── results/              # Backtest results
+└── tests/                # Tests
+```
+
+## Training ML Models
+
+```bash
+# Train price prediction models
+python -m app.ml.training.cli price --horizons 1 5 15 60
+
+# Train RL battery policy
+python -m app.ml.training.cli rl --episodes 1000
+```
+
+## Running Tests
+
+```bash
+pytest
+```