Fix short flags, AllowTCP wiring, invalid root server error, add config tests

- Register -v/-q short flag aliases sharing the same bool variable as
  --verbose/--quiet so both forms work identically
- Register -d and -dd flags; use ParseDebugLevel() helper so -d sets
  Debug=1 and -dd sets Debug=2; remove the broken strings.Count approach
- Add AllowTCP field to dns.QueryConfig; guard TCP truncation fallback in
  QueryWithExchange and IterativeQueryWithExchange behind cfg.AllowTCP;
  wire cfg.AllowTCP from CLI config into QueryConfig in main.go
- ParseRootServer() now returns ErrInvalidRootServer instead of (nil,nil)
  when the string is non-empty but net.ParseIP fails
- Add internal/config/config_test.go covering ParseQueryType, ParseUDPSize,
  Validate, GetDomain, ParseRootServer, ParseDebugLevel, and the
  --always-tcp/--allow-tcp cross-check
- Add TestQueryNoTCPFallbackWhenDisabled to dns/query_test.go
- Update existing truncation tests to set AllowTCP:true
- Add TODO comments on display flags not yet wired to output layer

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

cmd/exploredns/main.go

@@ -5,7 +5,6 @@ import (
 	"flag"
 	"fmt"
 	"os"
-	"strings"
 	"time"
 
 	"github.com/hits/ExploreDNS/internal/config"
@@ -27,22 +26,42 @@ func main() {
 	maxDepth := flag.Int("max-depth", cfg.MaxDepth, "Max traversal depth (1-100)")
 	retries := flag.Int("retries", cfg.Retries, "Retry count (0-10)")
 	fast := flag.Bool("fast", cfg.Fast, "Fast mode: reuse earlier branch cache")
-	verbose := flag.Bool("verbose", cfg.Verbose, "Verbose output")
-	debugFlag := flag.Bool("debug", false, "Debug mode (stackable: -dd for library debug)")
-	quiet := flag.Bool("quiet", cfg.Quiet, "Suppress supplementary info")
 
+	// Verbose: long and short form share the same variable.
+	var verboseVal bool
+	flag.BoolVar(&verboseVal, "verbose", cfg.Verbose, "Verbose output")
+	flag.BoolVar(&verboseVal, "v", cfg.Verbose, "Verbose output (shorthand)")
+
+	// Debug: -d sets level 1, -dd sets level 2 (library debug).
+	var dFlag, ddFlag bool
+	flag.BoolVar(&dFlag, "d", false, "Debug mode (stackable: -dd for library debug)")
+	flag.BoolVar(&dFlag, "debug", false, "Debug mode")
+	flag.BoolVar(&ddFlag, "dd", false, "Library debug mode (equivalent to -d -d)")
+
+	// Quiet: long and short form share the same variable.
+	var quietVal bool
+	flag.BoolVar(&quietVal, "quiet", cfg.Quiet, "Suppress supplementary info")
+	flag.BoolVar(&quietVal, "q", cfg.Quiet, "Suppress supplementary info (shorthand)")
+
+	// TODO: ShowProgress is parsed but not yet wired to the traversal/output layer.
 	showProgress := flag.Bool("show-progress", cfg.ShowProgress, "Show traversal progress")
 	noShowProgress := flag.Bool("no-show-progress", false, "Hide traversal progress")
+	// TODO: ShowResolves is parsed but not yet wired to the traversal/output layer.
 	showResolves := flag.Bool("show-resolves", cfg.ShowResolves, "Show glue resolution details")
 	noShowResolves := flag.Bool("no-show-resolves", false, "Hide glue resolution details")
+	// TODO: ShowServers is parsed but not yet wired to the traversal/output layer.
 	showServers := flag.Bool("show-servers", cfg.ShowServers, "Show servers queried")
 	noShowServers := flag.Bool("no-show-servers", false, "Hide servers queried")
+	// TODO: ShowVersions is parsed but not yet wired to the traversal/output layer.
 	showVersions := flag.Bool("show-versions", cfg.ShowVersions, "Show server versions")
 	noShowVersions := flag.Bool("no-show-versions", false, "Hide server versions")
+	// TODO: ShowAllStats is parsed but not yet wired to the traversal/output layer.
 	showAllStats := flag.Bool("show-all-stats", cfg.ShowAllStats, "Show all statistics")
 	noShowAllStats := flag.Bool("no-show-all-stats", false, "Hide all statistics")
+	// TODO: ShowResults is partially wired; full structured output is pending.
 	showResults := flag.Bool("show-results", cfg.ShowResults, "Show query results")
 	noShowResults := flag.Bool("no-show-results", false, "Hide query results")
+	// TODO: ShowSummaryResults is parsed but not yet wired to the traversal/output layer.
 	showSummaryResults := flag.Bool("show-summary-results", cfg.ShowSummaryResults, "Show summary of results")
 	noShowSummaryResults := flag.Bool("no-show-summary-results", false, "Hide summary of results")
 
@@ -52,16 +71,6 @@ func main() {
 
 	args := flag.Args()
 
-	debugLevel := 0
-	for _, arg := range os.Args[1:] {
-		if strings.Count(arg, "-d") > 0 || strings.Count(arg, "-dd") > 0 {
-			debugLevel = strings.Count(arg, "-d") + strings.Count(arg, "-dd")
-		}
-	}
-	if *debugFlag {
-		debugLevel++
-	}
-
 	cfg.QueryType = *queryType
 	cfg.RootServer = *rootServer
 	cfg.AllRootServers = *allRootServers
@@ -73,9 +82,9 @@ func main() {
 	cfg.MaxDepth = *maxDepth
 	cfg.Retries = *retries
 	cfg.Fast = *fast
-	cfg.Verbose = *verbose
-	cfg.Debug = debugLevel
-	cfg.Quiet = *quiet
+	cfg.Verbose = verboseVal
+	cfg.Debug = config.ParseDebugLevel(dFlag, ddFlag)
+	cfg.Quiet = quietVal
 
 	if *noShowProgress {
 		cfg.ShowProgress = false
@@ -142,10 +151,11 @@ func main() {
 	}
 
 	queryConfig := &dns.QueryConfig{
-		UDPSize: cfg.UDPSize,
-		Timeout: 5 * time.Second,
-		Retries: cfg.Retries,
-		UseTCP:  cfg.AlwaysTCP,
+		UDPSize:  cfg.UDPSize,
+		Timeout:  5 * time.Second,
+		Retries:  cfg.Retries,
+		UseTCP:   cfg.AlwaysTCP,
+		AllowTCP: cfg.AllowTCP,
 	}
 
 	rootConfig := &dns.RootDiscoveryConfig{