docs: comprehensive documentation for ExploreDNS

- Rewrite README.md with overview, features, installation (go install +
  build from source), quick start, full CLI flag reference table,
  output section descriptions, project structure, and development guide

- Add package-level doc comments to all five internal packages:
  config, dns, fingerprint, output, traverse (via doc.go or existing
  package-declaration files)

- Add GoDoc comments on every exported type, constant, function, and
  method across all packages:
  - internal/config: Config struct fields, all Parse*/Default/Validate
  - internal/dns: QueryConfig, Resolver, BasicResolver, CachingResolver,
    ExchangeFunc, RootServer, RootDiscoveryConfig, DecodedResponse,
    ResponseClassification, all exported helpers
  - internal/fingerprint: Fingerprinter, New, NewWithTimeout, Query,
    FingerprintAll
  - internal/traverse: Traverser, TraverserConfig, TraversalResult,
    Referral, ResolutionState, Response, ResponseType, InfoCache,
    Stack, TraverserHooks, EventStage, TraversalEvent, EventHandler,
    CircularReferralError, UnresolvableNameserverError
  - internal/output: Format, Config, Formatter, SummaryStats,
    NewFormatter, AttachHooks, RunTraversal, DefaultConfig,
    ComputeSummary

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Co-authored-by: multica-agent <github@multica.ai>

internal/output/formatter.go

@@ -8,34 +8,53 @@ import (
 	"github.com/hits/ExploreDNS/internal/traverse"
 )
 
+// Format selects the output format.
 type Format int
 
+// Output format constants.
 const (
-	FormatText Format = iota
-	FormatJSON
+	FormatText Format = iota // human-readable coloured text (default)
+	FormatJSON               // machine-readable JSON
 )
 
+// Config carries settings that control what the formatter emits.
 type Config struct {
-	Format             Format
-	Domain             string
-	QueryType          string
-	ShowProgress       bool
-	ShowResolves       bool
-	ShowServers        bool
-	ShowVersions       bool
-	ShowAllStats       bool
-	ShowResults        bool
+	// Format selects text or JSON output.
+	Format Format
+	// Domain is the queried domain name, included in JSON output.
+	Domain string
+	// QueryType is the record type queried, included in JSON output.
+	QueryType string
+	// ShowProgress enables per-referral progress lines.
+	ShowProgress bool
+	// ShowResolves enables nameserver resolution detail lines.
+	ShowResolves bool
+	// ShowServers enables the server list section.
+	ShowServers bool
+	// ShowVersions enables version.bind fingerprint display alongside servers.
+	ShowVersions bool
+	// ShowAllStats enables per-result stats as they arrive (in text mode).
+	ShowAllStats bool
+	// ShowResults enables the terminal-results section.
+	ShowResults bool
+	// ShowSummaryResults enables the probability summary section.
 	ShowSummaryResults bool
-	Verbose            bool
-	Quiet              bool
-	Color              bool
-	Debug              int
+	// Verbose enables additional detail in progress lines.
+	Verbose bool
+	// Quiet suppresses the introductory banner line.
+	Quiet bool
+	// Color enables ANSI terminal colour codes in text output.
+	Color bool
+	// Debug controls debug verbosity for the formatter itself.
+	Debug int
 
 	// Fingerprints maps server IP strings to their version.bind version strings.
 	// Populated by RunTraversal when ShowVersions and ShowServers are both true.
 	Fingerprints map[string]string
 }
 
+// DefaultConfig returns a Config with all output sections enabled, text format,
+// and color determined by the NO_COLOR environment variable.
 func DefaultConfig() *Config {
 	return &Config{
 		Format:             FormatText,
@@ -50,14 +69,23 @@ func DefaultConfig() *Config {
 	}
 }
 
+// Formatter is the interface that both the text and JSON output backends implement.
+// Each method is called by the traversal hooks or by RunTraversal.
 type Formatter interface {
+	// WriteProgress is called at EventStart for each Referral.
 	WriteProgress(event traverse.TraversalEvent) error
+	// WriteResolve is called at EventStart for nameserver resolution sub-steps.
 	WriteResolve(event traverse.TraversalEvent) error
+	// WriteResult is called at EventComplete for each TraversalResult.
 	WriteResult(result traverse.TraversalResult) error
+	// WriteSummary is called once after all results are collected.
 	WriteSummary(results []traverse.TraversalResult) error
+	// Flush finalises output (e.g. writes buffered JSON to the writer).
 	Flush() error
 }
 
+// NewFormatter returns the appropriate Formatter (text or JSON) based on cfg.Format.
+// A nil cfg uses DefaultConfig.  A nil w uses os.Stdout.
 func NewFormatter(cfg *Config, w io.Writer) Formatter {
 	if cfg == nil {
 		cfg = DefaultConfig()
@@ -71,6 +99,8 @@ func NewFormatter(cfg *Config, w io.Writer) Formatter {
 	return newTextFormatter(cfg, w)
 }
 
+// AttachHooks creates a TraverserHooks that routes traversal events to formatter
+// according to cfg visibility settings.  Returns nil when cfg or formatter is nil.
 func AttachHooks(cfg *Config, formatter Formatter) *traverse.TraverserHooks {
 	if cfg == nil || formatter == nil {
 		return nil