fix: banking shell screen rendering artifacts and transfer panic

Fix rendering issues where content from previous screens bled through
when switching between views of different heights/widths:

- Pad every line to full terminal width (ANSI-aware) so shorter lines
  overwrite leftover content from previous renders
- Track terminal height via WindowSizeMsg and pad between content and
  footer to fill the screen
- Send tea.ClearScreen on all screen transitions for height changes
- Fix panic in transfer completion when routing number is < 4 chars

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

internal/shell/banking/style.go

@@ -100,11 +100,33 @@ func formatCurrency(cents int64) string {
 	return fmt.Sprintf("$%s.%02d", ds, remainder)
 }
 
+// padLine pads a single line (which may contain ANSI codes) to termWidth
+// using its visual width.
+func padLine(line string) string {
+	w := lipgloss.Width(line)
+	if w >= termWidth {
+		return line
+	}
+	return line + strings.Repeat(" ", termWidth-w)
+}
+
+// padLines pads every line in a multi-line string to termWidth so that
+// shorter lines fully overwrite previous content in the terminal.
+func padLines(s string) string {
+	lines := strings.Split(s, "\n")
+	for i, line := range lines {
+		lines[i] = padLine(line)
+	}
+	return strings.Join(lines, "\n")
+}
+
 // screenFrame wraps content in the persistent header and footer.
-func screenFrame(bankName, terminalID, region, content string) string {
+// The height parameter is used to pad the output to fill the terminal,
+// preventing leftover lines from previous renders bleeding through.
+func screenFrame(bankName, terminalID, region, content string, height int) string {
 	var b strings.Builder
 
-	// Header.
+	// Header (4 lines).
 	b.WriteString(divider())
 	b.WriteString("\n")
 	b.WriteString(centerText(bankName + " FEDERAL RESERVE SYSTEM"))
@@ -117,12 +139,29 @@ func screenFrame(bankName, terminalID, region, content string) string {
 	// Content.
 	b.WriteString(content)
 
-	// Footer.
+	// Pad with blank lines between content and footer so the footer
+	// stays at the bottom and the total output fills the terminal height.
+	if height > 0 {
+		const headerLines = 4
+		const footerLines = 2
+		// 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)
+		for i := used; i < height; i++ {
+			b.WriteString(blankLine)
+			b.WriteString("\n")
+		}
+	}
+
+	// Footer (2 lines).
 	b.WriteString("\n")
 	b.WriteString(divider())
 	b.WriteString("\n")
 	footer := fmt.Sprintf(" TERMINAL: %s | REGION: %s | ENCRYPTED SESSION ACTIVE", terminalID, region)
 	b.WriteString(dimStyle.Render(padRight(footer, termWidth)))
 
-	return b.String()
+	// Pad every line to full terminal width so shorter lines overwrite
+	// leftover content from previous renders.
+	return padLines(b.String())
 }