fix: FR collector use premiumIndex API for real-time 5min data

- Changed from /fapi/v1/fundingRate (8h settlement only) to /fapi/v1/premiumIndex (real-time)
- Each 5-min poll now stores a new row with current timestamp
- Payload includes both fundingRate and lastFundingRate for compat
- Fixes: FR data was only 6 rows per 4 days, now ~288/day per coin

backend/market_data_collector.py

@@ -136,13 +136,25 @@ class MarketDataCollector:
         self.save_indicator(symbol, "coinbase_premium", ts, payload)
 
     async def collect_funding_rate(self, session: aiohttp.ClientSession, symbol: str) -> None:
-        endpoint = "https://fapi.binance.com/fapi/v1/fundingRate"
+        endpoint = "https://fapi.binance.com/fapi/v1/premiumIndex"
-        data = await self.fetch_json(session, endpoint, {"symbol": symbol, "limit": 1})
+        data = await self.fetch_json(session, endpoint, {"symbol": symbol})
         if not data:
             raise RuntimeError("empty response")
-        item = data[0]
+        # premiumIndex returns a single object (not array)
-        ts = int(item.get("fundingTime") or int(time.time() * 1000))
+        item = data if isinstance(data, dict) else data[0]
-        self.save_indicator(symbol, "funding_rate", ts, item)
+        # Use current time as timestamp so every 5-min poll stores a new row
+        ts = int(time.time() * 1000)
+        payload = {
+            "symbol": item.get("symbol"),
+            "markPrice": item.get("markPrice"),
+            "indexPrice": item.get("indexPrice"),
+            "lastFundingRate": item.get("lastFundingRate"),
+            "nextFundingTime": item.get("nextFundingTime"),
+            "interestRate": item.get("interestRate"),
+            "fundingRate": item.get("lastFundingRate"),  # compat: signal_engine reads 'fundingRate'
+            "time": ts,
+        }
+        self.save_indicator(symbol, "funding_rate", ts, payload)
 
     async def collect_symbol(self, session: aiohttp.ClientSession, symbol: str) -> None:
         tasks = [