fix: add background snapshot loop - collect every 2s regardless of frontend

backend/main.py

@@ -73,9 +73,35 @@ def save_snapshot(rates: dict):
         pass  # 落库失败不影响API响应
 
 
+async def background_snapshot_loop():
+    """后台每2秒自动拉取费率+价格并落库，不依赖前端调用"""
+    while True:
+        try:
+            async with httpx.AsyncClient(timeout=5, headers=HEADERS) as client:
+                tasks = [client.get(f"{BINANCE_FAPI}/premiumIndex", params={"symbol": s}) for s in SYMBOLS]
+                responses = await asyncio.gather(*tasks, return_exceptions=True)
+            result = {}
+            for sym, resp in zip(SYMBOLS, responses):
+                if isinstance(resp, Exception) or resp.status_code != 200:
+                    continue
+                data = resp.json()
+                key = sym.replace("USDT", "")
+                result[key] = {
+                    "lastFundingRate": float(data["lastFundingRate"]),
+                    "markPrice": float(data["markPrice"]),
+                    "indexPrice": float(data["indexPrice"]),
+                }
+            if result:
+                save_snapshot(result)
+        except Exception:
+            pass
+        await asyncio.sleep(2)
+
+
 @app.on_event("startup")
 async def startup():
     init_db()
+    asyncio.create_task(background_snapshot_loop())
 
 
 @app.get("/api/health")