fix(tui): render sparkline 2 chars narrower than column to prevent wrapping

Cell padding inside the table causes sparkline content at full column
width to wrap. Subtract 2 from sparkWidth for content rendering.

internal/tui/tab_sites.go

@@ -418,7 +418,10 @@ func (m Model) viewSitesTab() string {
 
 	layout := m.computeLayout()
 	nameW := layout.nameW
-	sparkWidth := layout.sparkW
+	sparkWidth := layout.sparkW - 2
+	if sparkWidth < 8 {
+		sparkWidth = 8
+	}
 
 	var groupRows map[int]bool
 	return m.renderTable(