feat: add testnet mode support and fix UDS order type classification

- Add BINANCE_TESTNET env var to switch between live/demo API keys
- Add KLINE_INTERVAL env var (default 15m) for configurable candle interval
- Pass testnet flag through to Exchange, DataStream, UDS, Notifier
- Add demo mode in bot: forced LONG entry with fixed 0.5% SL / 2% TP
- Fix UDS close_reason: use ot (original order type) field to correctly
  classify STOP_MARKET/TAKE_PROFIT_MARKET triggers (was MANUAL)
- Add UDS raw event logging with ot field for debugging
- Add backtest market context (BTC/ETH regime, L/S ratio per fold)
- Separate testnet trade history to data/trade_history/testnet/

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/data_stream.py

@@ -77,10 +77,11 @@ class KlineStream:
             })
         logger.info(f"과거 캔들 {len(self.buffer)}개 로드 완료 — 즉시 신호 계산 가능")
 
-    async def start(self, api_key: str, api_secret: str):
+    async def start(self, api_key: str, api_secret: str, testnet: bool = False):
         client = await AsyncClient.create(
             api_key=api_key,
             api_secret=api_secret,
+            demo=testnet,
         )
         await self._preload_history(client)
         bm = BinanceSocketManager(client)
@@ -189,10 +190,11 @@ class MultiSymbolStream:
             self._preload_one(client, symbol, limit) for symbol in self.symbols
         ])
 
-    async def start(self, api_key: str, api_secret: str):
+    async def start(self, api_key: str, api_secret: str, testnet: bool = False):
         client = await AsyncClient.create(
             api_key=api_key,
             api_secret=api_secret,
+            demo=testnet,
         )
         await self._preload_history(client)
         bm = BinanceSocketManager(client)