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

middleware/validation.py

@@ -0,0 +1,13 @@
+from fastapi import Request, HTTPException
+
+
+async def validate_json(request: Request, call_next):
+    # Only validate JSON for requests with a body
+    if request.method in ("POST", "PUT", "PATCH"):
+        try:
+            # attempt to parse json body
+            await request.json()
+        except Exception:
+            raise HTTPException(status_code=400, detail="Invalid JSON payload")
+    response = await call_next(request)
+    return response