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/traverse/traverse.go

@@ -1 +1,17 @@
+// Package traverse implements iterative DNS tree traversal.
+//
+// Starting from the DNS root, the traverser follows referrals depth-first until
+// it reaches a terminal response (answer, NXDOMAIN, SERVFAIL, etc.) for the
+// queried name and type.  CNAME chains are followed automatically; CNAME loops
+// are detected and reported as errors.
+//
+// Key types:
+//
+//   - Traverser      — entry point; call NewTraverser then Traverse.
+//   - TraverserConfig — controls max depth, query type, root discovery and fast mode.
+//   - Referral        — a pending query to a set of nameserver addresses.
+//   - Response        — the classified, decoded result of querying a Referral.
+//   - InfoCache        — a two-level (parent/child) cache for NS records and glue.
+//   - Stack            — depth-limited LIFO work queue used by Traverser.
+//   - TraverserHooks   — callback interface for progress and result events.
 package traverse