feat(tui): mouse click for settings sections, column sort, logs panel

- Click Alerts/Nodes/Users sub-tabs in settings to switch sections
- Click STATUS/NAME/LATENCY column headers to sort (click again
  to reverse direction)
- Logs panel show/hide: [l] toggles sidebar visibility, click
  focused panel to hide. Monitors expand to full width when hidden.
- Logs full-screen: Enter when focused on logs opens scrollable
  full-screen log view with severity tags, filter toggle [f],
  and live updates

internal/tui/tab_sites.go

@@ -110,6 +110,11 @@ func (m Model) computeLayout() tableLayout {
 		sortName:    colName,
 		sortLatency: colLatency,
 	}
+	sortableKeys := map[colKey]string{
+		colStatus:  "sort-status",
+		colName:    "sort-name",
+		colLatency: "sort-latency",
+	}
 	if sortedKey, ok := sortColMap[m.sortColumn]; ok {
 		arrow := "▼"
 		if m.sortAsc {
@@ -122,6 +127,11 @@ func (m Model) computeLayout() tableLayout {
 			}
 		}
 	}
+	for i, k := range active {
+		if zoneID, ok := sortableKeys[k]; ok {
+			headers[i] = m.zones.Mark(zoneID, headers[i])
+		}
+	}
 
 	numCols := len(headers)
 	borderOverhead := 2 + (numCols - 1)