fix: improve test isolation and configuration

- Use in-memory SQLite for tests to prevent conflicts
- Add try/finally for robust test cleanup
- Make database URL configurable via env var
- Make CORS origins configurable via env var
- Make SQL echo configurable via env var

backend/app/main.py

@@ -1,3 +1,4 @@
+import os
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from contextlib import asynccontextmanager
@@ -18,7 +19,7 @@ app = FastAPI(
 
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=["http://localhost:3000"],
+    allow_origins=os.environ.get("CORS_ORIGINS", "http://localhost:3000").split(","),
     allow_credentials=True,
     allow_methods=["*"],
     allow_headers=["*"],