feat: implement output formatting and display (HAN-383)

Add text and JSON formatters with real-time progress via traverser hooks,
summary statistics, and CLI integration for --show-* and --json flags.

Co-authored-by: multica-agent <github@multica.ai>

internal/traverse/hooks_test.go

@@ -0,0 +1,52 @@
+package traverse
+
+import (
+	"context"
+	"net"
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestTraverserHooksEmitEvents(t *testing.T) {
+	answerResp := func() *dns.Msg {
+		m := new(dns.Msg)
+		m.SetReply(new(dns.Msg))
+		m.Answer = append(m.Answer, &dns.A{
+			Hdr: dns.RR_Header{Name: "example.com.", Rrtype: dns.TypeA, Class: dns.ClassINET, Ttl: 300},
+			A:   net.ParseIP("93.184.216.34"),
+		})
+		return m
+	}()
+
+	var events []TraversalEvent
+	hooks := &TraverserHooks{
+		OnEvent: func(event TraversalEvent) {
+			events = append(events, event)
+		},
+	}
+
+	tr := NewTraverser(&TraverserConfig{
+		MaxDepth:  5,
+		QueryType: dns.TypeA,
+		RootAddrs: []net.IP{net.ParseIP("198.41.0.4")},
+		Hooks:     hooks,
+	})
+	tr.SetExchange(func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
+		return answerResp.Copy(), nil
+	})
+
+	_, err := tr.Traverse(context.Background(), "example.com")
+	if err != nil {
+		t.Fatalf("Traverse: %v", err)
+	}
+	if len(events) < 2 {
+		t.Fatalf("expected start and complete events, got %d", len(events))
+	}
+	if events[0].Stage != EventStart {
+		t.Fatalf("first event stage = %v, want start", events[0].Stage)
+	}
+	if events[1].Stage != EventComplete {
+		t.Fatalf("second event stage = %v, want complete", events[1].Stage)
+	}
+}