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/doc.go

@@ -0,0 +1,14 @@
+// Package output formats ExploreDNS traversal results for human-readable text
+// and machine-readable JSON output.
+//
+// The Formatter interface is the single point of contact for the traversal
+// engine.  Two implementations are provided:
+//
+//   - text formatter (default) — coloured, human-readable output.
+//   - JSON formatter (--json flag) — structured JSON suitable for piping.
+//
+// NewFormatter selects the right implementation based on Config.Format.
+// RunTraversal is the high-level entry point: it attaches event hooks,
+// executes the traversal, fingerprints encountered servers, and writes the
+// final summary and flush.
+package output