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/output/formatter.go

@@ -0,0 +1,85 @@
+package output
+
+import (
+	"io"
+	"os"
+
+	"github.com/hits/ExploreDNS/internal/traverse"
+)
+
+type Format int
+
+const (
+	FormatText Format = iota
+	FormatJSON
+)
+
+type Config struct {
+	Format             Format
+	Domain             string
+	QueryType          string
+	ShowProgress       bool
+	ShowResolves       bool
+	ShowServers        bool
+	ShowVersions       bool
+	ShowAllStats       bool
+	ShowResults        bool
+	ShowSummaryResults bool
+	Verbose            bool
+	Quiet              bool
+	Color              bool
+}
+
+func DefaultConfig() *Config {
+	return &Config{
+		Format:             FormatText,
+		ShowProgress:       true,
+		ShowResolves:       true,
+		ShowServers:        true,
+		ShowVersions:       true,
+		ShowAllStats:       true,
+		ShowResults:        true,
+		ShowSummaryResults: true,
+		Color:              os.Getenv("NO_COLOR") == "",
+	}
+}
+
+type Formatter interface {
+	WriteProgress(event traverse.TraversalEvent) error
+	WriteResolve(event traverse.TraversalEvent) error
+	WriteResult(result traverse.TraversalResult) error
+	WriteSummary(results []traverse.TraversalResult) error
+	Flush() error
+}
+
+func NewFormatter(cfg *Config, w io.Writer) Formatter {
+	if cfg == nil {
+		cfg = DefaultConfig()
+	}
+	if w == nil {
+		w = os.Stdout
+	}
+	if cfg.Format == FormatJSON {
+		return newJSONFormatter(cfg, w)
+	}
+	return newTextFormatter(cfg, w)
+}
+
+func AttachHooks(cfg *Config, formatter Formatter) *traverse.TraverserHooks {
+	if cfg == nil || formatter == nil {
+		return nil
+	}
+	return &traverse.TraverserHooks{
+		OnEvent: func(event traverse.TraversalEvent) {
+			switch {
+			case event.IsResolve && cfg.ShowResolves:
+				_ = formatter.WriteResolve(event)
+			case !event.IsResolve && cfg.ShowProgress:
+				_ = formatter.WriteProgress(event)
+			}
+			if event.Stage == traverse.EventComplete && cfg.ShowAllStats {
+				_ = formatter.WriteResult(event.Result)
+			}
+		},
+	}
+}