feat(tui): stable detail panel height with scroll support

Detail sidebar now maintains consistent height matching the monitors
panel across all modes (default, SLA, history). Content scrolls within
the fixed frame via mouse wheel or j/k when the detail panel is
focused. Scroll offset resets on mode/monitor/period changes. Logs
strip stays visible in all states.

internal/tui/tui.go

@@ -160,11 +160,12 @@ type Model struct {
 	historySiteName string
 	historySiteID   int
 
-	slaReport         monitor.SLAReport
-	slaDailyBreakdown []monitor.DayReport
-	slaSiteName       string
-	slaSiteID         int
-	slaPeriodIdx      int
+	slaReport          monitor.SLAReport
+	slaDailyBreakdown  []monitor.DayReport
+	slaSiteName        string
+	slaSiteID          int
+	slaPeriodIdx       int
+	detailScrollOffset int
 
 	isAdmin bool
 	zones   *zone.Manager