fix: apply black background to banking TUI padding areas

Padding spaces (end-of-line and blank filler lines) were unstyled,
causing the terminal's default background to bleed through.

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

internal/shell/banking/style.go

@@ -101,13 +101,14 @@ func formatCurrency(cents int64) string {
 }
 
 // padLine pads a single line (which may contain ANSI codes) to termWidth
-// using its visual width.
+// using its visual width. Padding uses a black background so the terminal's
+// default background doesn't bleed through.
 func padLine(line string) string {
 	w := lipgloss.Width(line)
 	if w >= termWidth {
 		return line
 	}
-	return line + strings.Repeat(" ", termWidth-w)
+	return line + baseStyle.Render(strings.Repeat(" ", termWidth-w))
 }
 
 // padLines pads every line in a multi-line string to termWidth so that
@@ -147,7 +148,7 @@ func screenFrame(bankName, terminalID, region, content string, height int) strin
 		// strings.Count gives newlines; add 1 for the line after the last \n.
 		contentLines := strings.Count(content, "\n") + 1
 		used := headerLines + contentLines + footerLines
-		blankLine := strings.Repeat(" ", termWidth)
+		blankLine := baseStyle.Render(strings.Repeat(" ", termWidth))
 		for i := used; i < height; i++ {
 			b.WriteString(blankLine)
 			b.WriteString("\n")