Bitcoin favicon, more strategies, default timeframe 5m

- Add an SVG Bitcoin favicon and link it in index.html.
- New indicators: macd() and roc().
- Five new strategies: macd_trend, bollinger_reversion, donchian_breakout,
  ema_cross, momentum (plus the existing sma_cross, rsi_reversion).
- Default TIMEFRAME is now 5m (config, .env.example, compose, workflow, UI).

backend/app/engine/strategies/bollinger_reversion.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+from typing import ClassVar
+
+from app.engine.strategies.base import Strategy, StrategyContext, register
+from app.models import PositionSide
+
+
+@register
+class BollingerReversion(Strategy):
+    """Buy the lower Bollinger band, exit at the middle band."""
+
+    key: ClassVar[str] = "bollinger_reversion"
+    name: ClassVar[str] = "Bollinger Reversion"
+    description: ClassVar[str] = (
+        "Enter long when the close falls below the lower Bollinger band and exit "
+        "when it returns to the middle band (SMA). Optional ATR stop."
+    )
+    default_params: ClassVar[dict] = {
+        "period": 20,
+        "num_std": 2.0,
+        "atr_period": 14,
+        "atr_stop_mult": 0.0,
+        "size": 1.0,
+    }
+    param_help: ClassVar[dict] = {
+        "period": "Bollinger lookback",
+        "num_std": "Band width in standard deviations",
+        "atr_period": "ATR lookback for the stop",
+        "atr_stop_mult": "Stop distance in ATRs (0 disables)",
+        "size": "Fraction of equity per trade",
+    }
+    param_bounds: ClassVar[dict] = {
+        "period": (5, 100),
+        "num_std": (0.5, 4.0),
+        "atr_stop_mult": (0.0, 10.0),
+        "size": (0.01, 1.0),
+    }
+
+    def on_candle(self, ctx: StrategyContext) -> None:
+        period = int(self.params["period"])
+        if len(ctx.closes) < period:
+            return
+        middle = ctx.sma(period)
+        deviation = ctx.std(period)
+        if middle is None or deviation is None:
+            return
+        lower = middle - float(self.params["num_std"]) * deviation
+
+        if ctx.is_flat and ctx.price < lower:
+            stop = None
+            mult = float(self.params["atr_stop_mult"])
+            if mult > 0:
+                atr_value = ctx.atr(int(self.params["atr_period"]))
+                if atr_value:
+                    stop = ctx.price - mult * atr_value
+            ctx.enter_long(
+                size=float(self.params["size"]),
+                stop_loss=stop,
+                reason="close below lower band",
+            )
+        elif ctx.side == PositionSide.LONG and ctx.price >= middle:
+            ctx.close(reason="close back at middle band")