feat: interactive score history chart with time range selector + BTC price overlay

- Time range buttons: 30D, 90D, 6M, 1Y, 2Y, 4Y, ALL
- BTC price overlay on right y-axis (orange dashed line)
- Accumulation zone backgrounds (green/yellow/red shading)
- Threshold lines at 65, 50, 35
- Tooltip shows score + zone label + BTC price
- Uses backtest daily_scores for full history (not just score_history.jsonl)
- Smart downsampling: daily for last 2yr, weekly before that
- Chart height increased to 320px

backtesting/engine.py

@@ -416,11 +416,17 @@ def run_backtest():
         }
 
     # --- Build time series for charting ---
-    # Downsample to weekly for chart efficiency
+    # Smart downsampling: daily for last 2 years, weekly before that
     chart_data = []
+    cutoff_2yr = daily_scores[-1]["date"][:4]  # rough 2yr cutoff
+    try:
+        from datetime import datetime as dt, timedelta
+        cutoff_date = (dt.strptime(daily_scores[-1]["date"], "%Y-%m-%d") - timedelta(days=730)).strftime("%Y-%m-%d")
+    except:
+        cutoff_date = "2024-01-01"
     for i, d in enumerate(daily_scores):
-        # Include every 7th day + last day
-        if i % 7 == 0 or i == len(daily_scores) - 1:
+        is_recent = d["date"] >= cutoff_date
+        if is_recent or i % 7 == 0 or i == len(daily_scores) - 1:
             chart_data.append({
                 "date": d["date"],
                 "score": d["score"],