fix(dashboard): current spread sign for HL→BG positions

Bug: current spread always computed as (hl-bg)/bg regardless of
position direction. For HL→BG positions, spread should be (bg-hl)/hl
to match entry spread convention.

Fix: check LongLeg.Exchange — if HL→BG, use (bg-hl)/hl instead.

web/static/style.css

@@ -126,6 +126,7 @@ td {
   white-space: nowrap;
 }
 tr:hover td { background: rgba(88, 166, 255, 0.05); }
+.trade-row { cursor: pointer; }
 .loading { text-align: center; color: var(--text-dim); padding: 20px !important; }
 
 .text-green { color: var(--green); }