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/tab_sites.go

@@ -132,6 +132,93 @@ func heartbeatSparkline(statuses []bool, width int) string {
 	return sb.String()
 }
 
+func (m Model) groupSparkline(groupID int, width int) string {
+	allSites := m.engine.GetAllSites()
+	var childStatuses [][]bool
+	for _, s := range allSites {
+		if s.ParentID == groupID && !s.Paused && !m.isMonitorInMaintenance(s.ID) {
+			hist, _ := m.engine.GetHistory(s.ID)
+			if len(hist.Statuses) > 0 {
+				childStatuses = append(childStatuses, hist.Statuses)
+			}
+		}
+	}
+
+	if len(childStatuses) == 0 {
+		return subtleStyle.Render(strings.Repeat("·", width))
+	}
+
+	maxLen := 0
+	for _, s := range childStatuses {
+		if len(s) > maxLen {
+			maxLen = len(s)
+		}
+	}
+	if maxLen > width {
+		maxLen = width
+	}
+
+	aggregated := make([]bool, maxLen)
+	for i := 0; i < maxLen; i++ {
+		allUp := true
+		for _, statuses := range childStatuses {
+			idx := len(statuses) - maxLen + i
+			if idx >= 0 && !statuses[idx] {
+				allUp = false
+				break
+			}
+		}
+		aggregated[i] = allUp
+	}
+
+	var sb strings.Builder
+	if remaining := width - len(aggregated); remaining > 0 {
+		sb.WriteString(subtleStyle.Render(strings.Repeat("·", remaining)))
+	}
+	for _, up := range aggregated {
+		if up {
+			sb.WriteString(specialStyle.Render("●"))
+		} else {
+			sb.WriteString(dangerStyle.Render("●"))
+		}
+	}
+	return sb.String()
+}
+
+func (m Model) groupUptime(groupID int) string {
+	allSites := m.engine.GetAllSites()
+	var allStatuses [][]bool
+	for _, s := range allSites {
+		if s.ParentID == groupID && !s.Paused && !m.isMonitorInMaintenance(s.ID) {
+			hist, _ := m.engine.GetHistory(s.ID)
+			if len(hist.Statuses) > 0 {
+				allStatuses = append(allStatuses, hist.Statuses)
+			}
+		}
+	}
+	if len(allStatuses) == 0 {
+		return subtleStyle.Render("—")
+	}
+	total, up := 0, 0
+	for _, statuses := range allStatuses {
+		for _, s := range statuses {
+			total++
+			if s {
+				up++
+			}
+		}
+	}
+	return fmtUptime(func() []bool {
+		out := make([]bool, total)
+		idx := 0
+		for _, statuses := range allStatuses {
+			copy(out[idx:], statuses)
+			idx += len(statuses)
+		}
+		return out
+	}())
+}
+
 func fmtLatency(d time.Duration) string {
 	ms := d.Milliseconds()
 	if ms == 0 {
@@ -227,7 +314,7 @@ func fmtStatus(status string, paused bool, inMaint bool) string {
 func (m Model) dynamicWidths() (nameW, sparkW int) {
 	fixed := 6 + 10 + 10 + 8 + 8 + 7 + 9 // #, TYPE, STATUS, LATENCY, UPTIME, SSL, RETRY
 	overhead := 30                       // cell padding + borders
-	avail := m.termWidth - 6 - fixed - overhead
+	avail := m.termWidth - chromePadH - 2 - fixed - overhead
 	if avail < 30 {
 		avail = 30
 	}
@@ -285,8 +372,8 @@ func (m Model) viewSitesTab() string {
 						"group",
 						fmtStatus(site.Status, site.Paused, m.isMonitorInMaintenance(site.ID)),
 						subtleStyle.Render("—"),
-						subtleStyle.Render("—"),
-						subtleStyle.Render(strings.Repeat("·", sparkWidth)),
+						m.groupUptime(site.ID),
+						m.groupSparkline(site.ID, sparkWidth),
 						subtleStyle.Render("-"),
 						subtleStyle.Render("—"),
 					})