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/macd_trend.py

@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+from typing import ClassVar
+
+from app.engine.indicators import macd
+from app.engine.strategies.base import Strategy, StrategyContext, register
+from app.models import PositionSide
+
+
+@register
+class MacdTrend(Strategy):
+    """MACD crossover trend following, long-only."""
+
+    key: ClassVar[str] = "macd_trend"
+    name: ClassVar[str] = "MACD Trend"
+    description: ClassVar[str] = (
+        "Open long when the MACD line crosses above its signal line and close when "
+        "it crosses back below."
+    )
+    default_params: ClassVar[dict] = {"fast": 12, "slow": 26, "signal": 9, "size": 1.0}
+    param_help: ClassVar[dict] = {
+        "fast": "Fast EMA period",
+        "slow": "Slow EMA period",
+        "signal": "Signal EMA period",
+        "size": "Fraction of equity per trade",
+    }
+    param_bounds: ClassVar[dict] = {"fast": (2, 100), "slow": (3, 200), "signal": (2, 100)}
+
+    def on_candle(self, ctx: StrategyContext) -> None:
+        closes = ctx.closes
+        if len(closes) < int(self.params["slow"]) + int(self.params["signal"]) + 2:
+            return
+        macd_line, signal_line, _ = macd(
+            closes,
+            int(self.params["fast"]),
+            int(self.params["slow"]),
+            int(self.params["signal"]),
+        )
+        m_prev, m_now = macd_line[-2], macd_line[-1]
+        s_prev, s_now = signal_line[-2], signal_line[-1]
+        if None in (m_prev, m_now, s_prev, s_now):
+            return
+
+        crossed_up = m_prev <= s_prev and m_now > s_now
+        crossed_down = m_prev >= s_prev and m_now < s_now
+
+        if ctx.is_flat and crossed_up:
+            ctx.enter_long(size=float(self.params["size"]), reason="MACD crossed above signal")
+        elif ctx.side == PositionSide.LONG and crossed_down:
+            ctx.close(reason="MACD crossed below signal")