feat: trading bot MVP — ICT Order Block + Liquidity Sweep strategy

Full-stack trading bot with:
- FastAPI backend with ICT strategy (Order Block + Liquidity Sweep detection)
- Backtester engine with rolling window, spread simulation, and performance metrics
- Hybrid market data service (yfinance + TwelveData with rate limiting + SQLite cache)
- Simulated exchange for paper trading
- React/TypeScript frontend with TradingView lightweight-charts v5
- Live dashboard with candlestick chart, OHLC legend, trade markers
- Backtest page with configurable parameters, equity curve, and trade table
- WebSocket support for real-time updates
- Bot runner with asyncio loop for automated trading

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/core/exchange/base.py

@@ -0,0 +1,88 @@
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+from datetime import datetime
+from typing import Optional
+
+import pandas as pd
+
+
+@dataclass
+class OrderResult:
+    trade_id: str
+    instrument: str
+    direction: str  # "buy" | "sell"
+    units: float
+    entry_price: float
+    stop_loss: float
+    take_profit: float
+    opened_at: datetime
+
+
+@dataclass
+class OpenTrade:
+    trade_id: str
+    instrument: str
+    direction: str
+    units: float
+    entry_price: float
+    stop_loss: float
+    take_profit: float
+    unrealized_pnl: float
+    opened_at: datetime
+
+
+@dataclass
+class AccountInfo:
+    balance: float
+    nav: float  # Net Asset Value
+    unrealized_pnl: float
+    currency: str
+
+
+class AbstractExchange(ABC):
+    """Interface commune pour tous les exchanges/brokers."""
+
+    @abstractmethod
+    async def get_candles(
+        self,
+        instrument: str,
+        granularity: str,
+        count: int = 200,
+        from_time: Optional[datetime] = None,
+        to_time: Optional[datetime] = None,
+    ) -> pd.DataFrame:
+        """
+        Retourne un DataFrame avec colonnes : time, open, high, low, close, volume.
+        """
+        ...
+
+    @abstractmethod
+    async def place_order(
+        self,
+        instrument: str,
+        units: float,  # positif = buy, négatif = sell
+        stop_loss: float,
+        take_profit: float,
+    ) -> OrderResult:
+        """Place un ordre au marché avec SL et TP."""
+        ...
+
+    @abstractmethod
+    async def close_trade(self, trade_id: str) -> float:
+        """Ferme un trade par son ID. Retourne le PnL réalisé."""
+        ...
+
+    @abstractmethod
+    async def get_open_trades(self) -> list[OpenTrade]:
+        """Retourne la liste des positions ouvertes."""
+        ...
+
+    @abstractmethod
+    async def get_account_info(self) -> AccountInfo:
+        """Retourne les infos du compte (solde, PnL, etc.)."""
+        ...
+
+    @abstractmethod
+    async def get_price(self, instrument: str) -> float:
+        """Retourne le prix mid actuel."""
+        ...