Add TP-Link AP support with wireless client sub-locations

- Add NodeType enum (switch, ap, wireless_client, wired_client)
- Poll SNMPv2c and SNMPv3 in parallel to win race with ping
- Render APs with bordered sub-locations containing wireless clients
- Fall back to parent interface stats when child lacks them
- Log when unreachable nodes become reachable via merge

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

nodes.go

@@ -388,6 +388,9 @@ func (n *Nodes) mergeNodes(keep, merge *Node) {
 		return
 	}
 
+	keepWasUnreachable := keep.Unreachable
+	mergeWasUnreachable := merge.Unreachable
+
 	for name := range merge.Names {
 		if keep.Names == nil {
 			keep.Names = NameSet{}
@@ -429,6 +432,26 @@ func (n *Nodes) mergeNodes(keep, merge *Node) {
 		merge.cancelFunc()
 	}
 
+	hasIPs := false
+	for _, iface := range keep.Interfaces {
+		if len(iface.IPs) > 0 {
+			hasIPs = true
+			break
+		}
+	}
+	if hasIPs && (keepWasUnreachable || mergeWasUnreachable) {
+		keep.Unreachable = false
+		if n.t != nil && n.t.errors != nil {
+			n.t.errors.RemoveUnreachable(keep)
+		}
+		if keepWasUnreachable {
+			log.Printf("[merge] %s is now reachable (merged with node that has IPs)", keep.DisplayName())
+		}
+		if mergeWasUnreachable {
+			log.Printf("[merge] %s is now reachable (merged into %s)", merge.DisplayName(), keep.DisplayName())
+		}
+	}
+
 	n.removeNode(merge)
 }