fix(tui): group selection highlight, layout constants, group history graphs

Group rows now show selection background when navigated to. Layout
chrome extracted to named constants to prevent viewport drift. Groups
display aggregate history as dot sparkline (●) distinct from site
bar sparklines, with uptime computed from active children only.
Paused and maintenance children excluded from group aggregates.

internal/tui/table_helpers.go

@@ -38,7 +38,7 @@ func (m Model) renderTable(headers []string, items int, buildRows func(start, en
 	selectedVisual := m.cursor - m.tableOffset
 	rows := buildRows(m.tableOffset, end)
 
-	tableWidth := m.termWidth - 6
+	tableWidth := m.termWidth - chromePadH - 2
 	if tableWidth < 40 {
 		tableWidth = 40
 	}
@@ -53,16 +53,21 @@ func (m Model) renderTable(headers []string, items int, buildRows func(start, en
 			if row == table.HeaderRow {
 				return tableHeaderStyle
 			}
+			isSelected := row == selectedVisual
 			if styleOverride != nil {
 				if s := styleOverride(row, col); s != nil {
-					if col < len(colWidths) && colWidths[col] > 0 {
-						return s.Width(colWidths[col])
+					style := *s
+					if isSelected {
+						style = tableSelectedStyle.Foreground(s.GetForeground())
 					}
-					return *s
+					if col < len(colWidths) && colWidths[col] > 0 {
+						style = style.Width(colWidths[col])
+					}
+					return style
 				}
 			}
 			base := tableCellStyle
-			if row == selectedVisual {
+			if isSelected {
 				base = tableSelectedStyle
 			}
 			if col < len(colWidths) && colWidths[col] > 0 {