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_test.go

@@ -110,10 +110,11 @@ func TestQueryTCPFallbackOnTruncation(t *testing.T) {
 	}
 
 	cfg := &QueryConfig{
-		UDPSize: 2048,
-		Timeout: 5,
-		Retries: 1,
-		UseTCP:  false,
+		UDPSize:  2048,
+		Timeout:  5,
+		Retries:  1,
+		UseTCP:   false,
+		AllowTCP: true,
 	}
 
 	server := net.ParseIP("8.8.8.8")
@@ -272,10 +273,11 @@ func TestQueryTCPFallbackFailsThenRetries(t *testing.T) {
 	}
 
 	cfg := &QueryConfig{
-		UDPSize: 2048,
-		Timeout: 5,
-		Retries: 2,
-		UseTCP:  false,
+		UDPSize:  2048,
+		Timeout:  5,
+		Retries:  2,
+		UseTCP:   false,
+		AllowTCP: true,
 	}
 
 	server := net.ParseIP("8.8.8.8")
@@ -287,3 +289,43 @@ func TestQueryTCPFallbackFailsThenRetries(t *testing.T) {
 		t.Errorf("expected 4 calls (2 retries x UDP+TCP), got %d", callCount)
 	}
 }
+
+func TestQueryNoTCPFallbackWhenDisabled(t *testing.T) {
+	truncatedResp := new(dns.Msg)
+	truncatedResp.Truncated = true
+	truncatedResp.SetReply(new(dns.Msg))
+
+	var mu sync.Mutex
+	calls := []bool{}
+	exchangeFn := func(ctx context.Context, server string, msg *dns.Msg, useTCP bool) (*dns.Msg, error) {
+		mu.Lock()
+		defer mu.Unlock()
+		calls = append(calls, useTCP)
+		return truncatedResp.Copy(), nil
+	}
+
+	cfg := &QueryConfig{
+		UDPSize:  2048,
+		Timeout:  5,
+		Retries:  1,
+		UseTCP:   false,
+		AllowTCP: false, // TCP fallback must be suppressed
+	}
+
+	server := net.ParseIP("8.8.8.8")
+	resp, err := QueryWithExchange(context.Background(), server, "example.com", TypeA, cfg, exchangeFn)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	// Only one UDP call; no TCP fallback.
+	if len(calls) != 1 {
+		t.Fatalf("expected 1 exchange call (no TCP fallback), got %d", len(calls))
+	}
+	if calls[0] != false {
+		t.Error("expected UDP-only call")
+	}
+	if !resp.Truncated {
+		t.Error("expected truncated response to be returned as-is")
+	}
+}
+