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/screen_transfer.go

@@ -165,8 +165,12 @@ func (m transferModel) View() string {
 		b.WriteString("\n\n")
 		b.WriteString(titleStyle.Render("  TRANSFER QUEUED FOR PROCESSING"))
 		b.WriteString("\n\n")
+		routing := m.transfer.RoutingNumber
+		if len(routing) > 4 {
+			routing = routing[:4]
+		}
 		b.WriteString(baseStyle.Render(fmt.Sprintf("  CONFIRMATION #: WR-%s-%s",
-			m.transfer.RoutingNumber[:4], "847291")))
+			routing, "847291")))
 		b.WriteString("\n")
 		b.WriteString(baseStyle.Render("  STATUS: PENDING FEDWIRE SETTLEMENT"))
 		b.WriteString("\n")