fix(tui): revert centering, fix demo GIF pacing

Revert upper-third centering — inconsistent start positions across tabs
felt jumpy. Back to standard top-align with consistent table placement.

Demo GIF now pauses on Nodes tab (cluster view is a selling point) and
skips Maint/Users quickly instead of sprinting through all three.

internal/tui/view_dashboard.go

@@ -181,18 +181,7 @@ func (m Model) viewDashboard() string {
 	if contentHeight < 1 {
 		contentHeight = 1
 	}
-
-	contentLines := lipgloss.Height(content)
-	var paddedContent string
-	if contentLines < contentHeight {
-		topPad := (contentHeight - contentLines) / 3
-		paddedContent = lipgloss.NewStyle().
-			PaddingTop(topPad).
-			Height(contentHeight).MaxHeight(contentHeight).
-			Render(content)
-	} else {
-		paddedContent = lipgloss.NewStyle().Height(contentHeight).MaxHeight(contentHeight).Render(content)
-	}
+	paddedContent := lipgloss.NewStyle().Height(contentHeight).MaxHeight(contentHeight).Render(content)
 
 	return outerPad.Render(lipgloss.JoinVertical(lipgloss.Top, header, paddedContent, footer))
 }