refacto: rename app into backend, to prepare for frontend dev

server/backend/adapters/http/main.py

@@ -0,0 +1,18 @@
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from .readings import readings_router
+
+app = FastAPI(title="SimuGazAPI", version="1.0.0")
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["*"],
+    allow_methods=["GET"],
+    allow_headers=["*"],
+)
+
+app.include_router(readings_router)
+
+@app.get("/health")
+def health():
+    return {"status": "ok"}