fix: hardcode steel blue border and bold for selected order card

Use explicit #4682B4 with bold to ensure the selected border is
visually distinct on all terminal themes including gruvbox.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/tui/account_orders.go

@@ -88,7 +88,7 @@ func (m Model) buildOrderCard(order models.Order, boxWidth int, isSelected bool)
 
 	var itemBox lipgloss.Style
 	if isSelected {
-		itemBox = base.BorderForeground(m.theme.Highlight())
+		itemBox = base.BorderForeground(lipgloss.Color("#4682B4")).Bold(true)
 	} else {
 		itemBox = base.BorderForeground(m.theme.Border())
 	}