Say each machine's last send in status and node show, and as fields in status --json (novox/hq issue 485)

The send record of issue 234 is now readable only through the controller's
verbs (issue 506), and only plan said it. status says per machine when it was
last sent a declaration, by whom, from which generation and what it answered;
node show says it in full with the refusal's words. A machine's answer is read
from its report only when that report is about the send and came after it.

cmd/mesh-controller/nodes.go

@@ -804,6 +804,19 @@ func showNode(ctx context.Context, stored *stores, name string) error {
 	if err := showMode(ctx, inv, node); err != nil {
 		return err
 	}
+	// What it was last sent, by whom, under which epoch, from which generation, naming which modules, and what
+	// it answered (novox/hq issue 485): the record of sends is read through this verb, never the store's reader.
+	// Unreadable is said, not taken for none.
+	switch last, found, err := inv.LastSend(ctx, name); {
+	case err != nil:
+		fmt.Printf("  what it was last sent could NOT be read: %v\n", err)
+	case !found:
+		fmt.Printf("  last sent         no send recorded since the mesh began keeping them\n")
+	default:
+		for _, line := range lastSendLines(last) {
+			fmt.Println(line)
+		}
+	}
 	// Whom agents run as here, and whether that account can become root without a person (ADR 0266).
 	for _, line := range agentAccountLines(ctx, inv, node) {
 		fmt.Println(line)