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/ema_cross.py

@@ -0,0 +1,60 @@
+from __future__ import annotations
+
+from typing import ClassVar
+
+from app.engine.indicators import ema, sma
+from app.engine.strategies.base import Strategy, StrategyContext, register
+from app.models import PositionSide
+
+
+@register
+class EmaCross(Strategy):
+    """EMA crossover with an optional long-term trend filter."""
+
+    key: ClassVar[str] = "ema_cross"
+    name: ClassVar[str] = "EMA Crossover"
+    description: ClassVar[str] = (
+        "Open long when the fast EMA crosses above the slow EMA (and price is "
+        "above the trend filter, if enabled); exit on the opposite cross."
+    )
+    default_params: ClassVar[dict] = {
+        "fast": 9,
+        "slow": 21,
+        "trend_filter": 200,
+        "size": 1.0,
+    }
+    param_help: ClassVar[dict] = {
+        "fast": "Fast EMA period",
+        "slow": "Slow EMA period",
+        "trend_filter": "SMA trend filter period (0 disables)",
+        "size": "Fraction of equity per trade",
+    }
+    param_bounds: ClassVar[dict] = {"fast": (2, 100), "slow": (3, 300), "size": (0.01, 1.0)}
+
+    def on_candle(self, ctx: StrategyContext) -> None:
+        fast_period = int(self.params["fast"])
+        slow_period = int(self.params["slow"])
+        trend_period = int(self.params["trend_filter"])
+        needed = max(slow_period, trend_period) + 2
+        if len(ctx.closes) < needed:
+            return
+
+        fast = ema(ctx.closes, fast_period)
+        slow = ema(ctx.closes, slow_period)
+        f_prev, f_now = fast[-2], fast[-1]
+        s_prev, s_now = slow[-2], slow[-1]
+        if None in (f_prev, f_now, s_prev, s_now):
+            return
+
+        trend_ok = True
+        if trend_period > 0:
+            trend = sma(ctx.closes, trend_period)[-1]
+            trend_ok = trend is not None and ctx.price > trend
+
+        crossed_up = f_prev <= s_prev and f_now > s_now
+        crossed_down = f_prev >= s_prev and f_now < s_now
+
+        if ctx.is_flat and crossed_up and trend_ok:
+            ctx.enter_long(size=float(self.params["size"]), reason="EMA cross up")
+        elif ctx.side == PositionSide.LONG and crossed_down:
+            ctx.close(reason="EMA cross down")