implement initial backend structure with authentication, user management, and database integration

backend/app/main.py

@@ -0,0 +1,44 @@
+from backend.app.routers import auth as auth_router
+from backend.app.routers import users as users_router
+from backend.app.routers import admin as admin_router
+from backend.app.db import close_db, init_db
+import os
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from dotenv import load_dotenv
+
+load_dotenv()
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    init_db()
+    yield
+    close_db()
+
+
+app = FastAPI(
+    title="AI Allucanget Biz API",
+    description="Multi-modal AI generation API powered by openrouter.ai",
+    version="0.1.0",
+    lifespan=lifespan,
+)
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=[os.getenv("CORS_ORIGINS", "http://localhost:5000")],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+app.include_router(auth_router.router)
+app.include_router(users_router.router)
+app.include_router(admin_router.router)
+
+
+@app.get("/health", tags=["health"])
+async def health() -> dict:
+    return {"status": "ok"}