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/tui.go

@@ -31,6 +31,16 @@ var (
 
 var pulseFrames = []string{"⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧", "⠇", "⠏"}
 
+const (
+	chromePadV   = 2 // outer Padding(1,2): 1 top + 1 bottom
+	chromePadH   = 4 // outer Padding(1,2): 2 left + 2 right
+	chromeHeader = 1 // tab bar line
+	chromeGaps   = 2 // "\n" separators: before content + before footer
+	chromeFooter = 2 // footer: "\n" prefix + text line
+	chromeTable  = 3 // renderTable "\n" prefix + top border + header + bottom border (lipgloss collapses two into three rendered lines)
+	chromeBase   = chromePadV + chromeHeader + chromeGaps + chromeFooter + chromeTable
+)
+
 type sessionState int
 
 const (
@@ -198,17 +208,16 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	case tea.WindowSizeMsg:
 		m.termWidth = msg.Width
 		m.termHeight = msg.Height
-		// Chrome: 1 top pad + 1 tabs + 2 newlines + 3 table borders + 1 table header + 1 footer + 1 bottom pad = 10
-		chrome := 10
-		if m.filterText != "" {
+		chrome := chromeBase
+		if m.filterMode || m.filterText != "" {
 			chrome++
 		}
 		m.maxTableRows = msg.Height - chrome
 		if m.maxTableRows < 1 {
 			m.maxTableRows = 1
 		}
-		m.logViewport.Width = msg.Width - 4
-		m.logViewport.Height = msg.Height - 8
+		m.logViewport.Width = msg.Width - chromePadH
+		m.logViewport.Height = msg.Height - (chromePadV + chromeHeader + chromeGaps + chromeFooter)
 		return m, tea.ClearScreen
 
 	case time.Time: