Add initial implementation of CalMiner with project structure, environment setup, and core features

- Create .env.example for environment variables
- Update README with project structure and development setup instructions
- Implement FastAPI application with API routes for scenarios and parameters
- Add database models for scenarios, parameters, and simulation results
- Introduce validation middleware for JSON requests
- Create services for running simulations and generating reports
- Add testing strategy and directory structure in documentation

config/database.py

@@ -0,0 +1,14 @@
+from sqlalchemy import create_engine
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy.orm import sessionmaker
+import os
+from dotenv import load_dotenv
+
+load_dotenv()
+DATABASE_URL = os.environ.get("DATABASE_URL")
+if not DATABASE_URL:
+    raise RuntimeError("DATABASE_URL environment variable is not set")
+
+engine = create_engine(DATABASE_URL, echo=True, future=True)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+Base = declarative_base()