Add pivot retest + engulfing strategy with dual take-profit

New strategy (pivot_retest_engulfing) that enters long/short trades at
pivot level retests confirmed by SMA 50 alignment and engulfing candle
patterns. Uses ATR-based stop loss with two take-profit levels — at TP1
half the position closes and SL moves to breakeven, at TP2 the rest closes.

- data_engine: add detect_engulfing() for bullish/bearish pattern detection
- backtester: add generate_signals_pivot_retest(), run_backtest_dual_tp(),
  update signal dispatcher and metrics for dual-TP trade format
- order_executor: support signal=-1 (SHORT), attach SL/TP levels
- config: switch to pivot_retest_engulfing with default params
- chart_trades: new mplfinance script to visualize entries on candlesticks
- README: rewrite with full setup guide, project structure, strategy docs
- requirements.txt: make portable (remove conda file:// paths), add mplfinance
- .env.example: add template for secrets

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

templates/chart.html

@@ -37,6 +37,7 @@
 (function() {
   var ohlc = {{ ohlc_json | safe }};
   var pivots = {{ pivot_json | safe }};
+  var smas = {{ sma_json | safe }};
 
   if (!ohlc || ohlc.length === 0) {
     document.getElementById('chart').innerHTML =
@@ -58,6 +59,26 @@
     name: '{{ instrument }}'
   }];
 
+  // SMA overlay lines
+  var smaColors = {
+    'sma_3':   '#ff9800',
+    'sma_20':  '#9c27b0',
+    'sma_21':  '#673ab7',
+    'sma_50':  '#00bcd4',
+    'sma_100': '#e91e63'
+  };
+  Object.keys(smas).forEach(function(key) {
+    traces.push({
+      x: times,
+      y: smas[key],
+      type: 'scatter',
+      mode: 'lines',
+      name: key.toUpperCase().replace('_', ' '),
+      line: {color: smaColors[key] || '#999', width: 1.5},
+      connectgaps: false
+    });
+  });
+
   // Pivot level lines
   var levelDefs = [
     {key: 'r3', color: '#b71c1c', label: 'R3'},