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/.gitignore

@@ -0,0 +1,46 @@
+.env
+.venv
+venv/
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+.pytest_cache/
+.coverage
+htmlcov/
+*.cover
+.hypothesis/
+.tox/
+.mypy_cache/
+.dmypy.json
+dmypy.json
+*.log
+logs/
+server.log
+*.pid
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+.DS_Store
+Thumbs.db
+*.bak
+*.tmp
+*.orig