feat(07-02): wire LoadResult into main.go and add --print-config flag

- Add printConfig bool var and --print-config flag registration
- runPrintConfig() early-exit before interface-required check (CFG-06)
- runLiveMode and runPcapMode accept config.LoadResult; user rules prepend via append(result.UserRules, classify.DefaultRules...)
- Remove unused synth import from main.go
- Add TestPrintConfigFlagRegistered, TestPrintConfigNoInterface, TestPrintConfigWithConfigFile
- newTestCmd() wires --print-config and --config flags through PersistentPreRunE

cmd/netsynth/main_test.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"bytes"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
@@ -16,6 +18,8 @@ func newTestCmd() *cobra.Command {
 	var testFilter string
 	var testRead string
 	var testOutput string
+	var testPrintConfig bool
+	var testConfigPath string
 
 	rootCmd := &cobra.Command{
 		Use:          "netsynth",
@@ -29,6 +33,8 @@ func newTestCmd() *cobra.Command {
 	rootCmd.Flags().StringVarP(&testOutput, "output", "o", "", "Output MP3 file path")
 	rootCmd.Flags().StringVar(&testFilter, "filter", "", "BPF filter expression")
 	rootCmd.Flags().StringVar(&testRead, "read", "", "Read packets from pcap file instead of live capture")
+	rootCmd.Flags().BoolVar(&testPrintConfig, "print-config", false, "Print effective config")
+	rootCmd.Flags().StringVar(&testConfigPath, "config", "", "Path to TOML config file")
 
 	// Wire test variables to package-level vars used by run()
 	rootCmd.PersistentPreRunE = func(cmd *cobra.Command, args []string) error {
@@ -38,6 +44,8 @@ func newTestCmd() *cobra.Command {
 		outputPath = testOutput
 		bpfFilter = testFilter
 		readPath = testRead
+		printConfig = testPrintConfig
+		configPath = testConfigPath
 		return nil
 	}
 
@@ -320,3 +328,72 @@ func TestHelpOutputNewFlags(t *testing.T) {
 		t.Errorf("expected help/usage output to contain '--read', usage: %s", usageStr)
 	}
 }
+
+// TestPrintConfigFlagRegistered verifies --print-config flag is registered.
+func TestPrintConfigFlagRegistered(t *testing.T) {
+	rootCmd := newTestCmd()
+	f := rootCmd.Flags().Lookup("print-config")
+	if f == nil {
+		t.Fatal("expected --print-config flag to be registered")
+	}
+}
+
+// TestPrintConfigNoInterface verifies --print-config works without -i flag.
+func TestPrintConfigNoInterface(t *testing.T) {
+	// Reset globals
+	ifaceName = ""
+	listIfaces = false
+	verbose = false
+	bpfFilter = ""
+	readPath = ""
+	outputPath = ""
+	printConfig = false
+	configPath = ""
+
+	// Use a temp dir with no netsynth.toml so no config is auto-discovered
+	t.Chdir(t.TempDir())
+
+	rootCmd := newTestCmd()
+	rootCmd.SetArgs([]string{"--print-config"})
+
+	var outBuf, errBuf bytes.Buffer
+	rootCmd.SetOut(&outBuf)
+	rootCmd.SetErr(&errBuf)
+
+	err := rootCmd.Execute()
+	if err != nil {
+		t.Fatalf("--print-config should not require -i, got error: %v", err)
+	}
+}
+
+// TestPrintConfigWithConfigFile verifies --print-config loads and displays a user config.
+func TestPrintConfigWithConfigFile(t *testing.T) {
+	// Create temp TOML with an override
+	dir := t.TempDir()
+	tomlPath := filepath.Join(dir, "test.toml")
+	if err := os.WriteFile(tomlPath, []byte("[sounds.ICMP]\nfrequency = 100.0\n"), 0644); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	// Reset globals
+	ifaceName = ""
+	listIfaces = false
+	verbose = false
+	bpfFilter = ""
+	readPath = ""
+	outputPath = ""
+	printConfig = false
+	configPath = ""
+
+	rootCmd := newTestCmd()
+	rootCmd.SetArgs([]string{"--print-config", "--config", tomlPath})
+
+	var outBuf, errBuf bytes.Buffer
+	rootCmd.SetOut(&outBuf)
+	rootCmd.SetErr(&errBuf)
+
+	err := rootCmd.Execute()
+	if err != nil {
+		t.Fatalf("--print-config with --config should succeed, got: %v", err)
+	}
+}