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>

internal/dns/query.go

@@ -10,18 +10,20 @@ import (
 )
 
 type QueryConfig struct {
-	UDPSize int
-	Timeout time.Duration
-	Retries int
-	UseTCP  bool
+	UDPSize  int
+	Timeout  time.Duration
+	Retries  int
+	UseTCP   bool
+	AllowTCP bool
 }
 
 func DefaultQueryConfig() *QueryConfig {
 	return &QueryConfig{
-		UDPSize: DefaultEDNS0UDPSize(),
-		Timeout: 5 * time.Second,
-		Retries: 3,
-		UseTCP:  false,
+		UDPSize:  DefaultEDNS0UDPSize(),
+		Timeout:  5 * time.Second,
+		Retries:  3,
+		UseTCP:   false,
+		AllowTCP: true,
 	}
 }
 
@@ -110,7 +112,7 @@ func QueryWithExchange(ctx context.Context, server net.IP, name string, qtype ui
 			continue
 		}
 
-		if resp.Truncated {
+		if resp.Truncated && cfg.AllowTCP {
 			resp, err = exchangeFn(ctx, serverStr, msg, true)
 			if err != nil {
 				lastErr = err
@@ -178,7 +180,7 @@ func IterativeQueryWithExchange(ctx context.Context, server net.IP, name string,
 			continue
 		}
 
-		if resp.Truncated {
+		if resp.Truncated && cfg.AllowTCP {
 			resp, err = exchangeFn(ctx, serverStr, msg, true)
 			if err != nil {
 				lastErr = err