fix(tui): quick wins batch — version footer, column widths, zebra, sparkline

- Show version in dashboard footer (wired from goreleaser ldflags)
- Cap name column at 35, raise sparkline minimum to 15 chars
- Preserve zebra background on group rows (was lost by style override)
- Group sparkline uses bullet • instead of heavy circle ●

internal/tui/tab_sites.go

@@ -78,13 +78,13 @@ func (m Model) computeLayout() tableLayout {
 	if nameW < 13 {
 		nameW = 13
 	}
-	if nameW > 40 {
-		nameW = 40
+	if nameW > 35 {
+		nameW = 35
 	}
 
 	sparkW := avail - nameW
-	if sparkW < 10 {
-		sparkW = 10
+	if sparkW < 15 {
+		sparkW = 15
 	}
 
 	widths[1] = nameW