config: autopilot to 4x 5x notional at 20x leverage; short floor 0.75 -> 0.4

Two independent changes bundled:
- Position sizing back to 4 positions x 5x equity notional at 20x leverage
  (20x total account notional, ~5% liquidation cushion) — aggressive book
  size by operator choice, for bigger single positions on a small account.
- Forced short-coverage signal floor lowered 0.75 -> 0.4. At 0.75, a
  long-leaning board left every bearish candidate below the bar, so no short
  ever opened and the book became a one-directional long bet. 0.4 keeps
  genuine directional signals so the book actually hedges — which matters
  more, not less, at 20x.

trader/auto_trader_force.go

@@ -8,11 +8,13 @@ import (
 )
 
 // forcedCoverageMinScore is the minimum absolute board z-score a candidate
-// needs before the engine will force-open it for book balance. Live trade
-// history showed forced entries on near-neutral signals (|z| < 0.3) were a
-// systematic money loser — especially shorts — while trades on strong signals
-// carried the edge. Below this bar the book is simply left unbalanced.
-const forcedCoverageMinScore = 0.75
+// needs before the engine will force-open it for book balance. Near-neutral
+// signals (|z| < ~0.3) proved a systematic loser, but a 0.75 floor was too
+// strict: in a long-leaning tape every bearish candidate scored below it, so
+// no short ever opened and the book became a one-directional long bet that
+// drew down hard. 0.4 keeps genuine directional signals while still filtering
+// pure noise, so the book can actually hedge.
+const forcedCoverageMinScore = 0.4
 
 // ensureLongShortCoverage tops the book up toward roughly half the
 // MaxPositions slots long and half short — but only with candidates whose