feat(06-02): add freqCfgs parameter to RunSynthesis

- Change RunSynthesis signature to accept injected config map (D-10)
- Replace hardcoded synth.ClassFreqConfigs with passed-in freqCfgs
- Update all three RunSynthesis calls in encode tests to pass synth.ClassFreqConfigs

encode/mp3_test.go

@@ -53,7 +53,7 @@ func TestMP3Valid(t *testing.T) {
 	tmpFile.Close()
 	defer os.Remove(tmpPath)
 
-	if err := RunSynthesis(snaps, tmpPath); err != nil {
+	if err := RunSynthesis(snaps, tmpPath, synth.ClassFreqConfigs); err != nil {
 		t.Fatalf("RunSynthesis: %v", err)
 	}
 
@@ -98,7 +98,7 @@ func TestZeroPacketError(t *testing.T) {
 	tmpPath := "/tmp/netsynth-should-not-exist-" + t.Name() + ".mp3"
 	defer os.Remove(tmpPath)
 
-	err := RunSynthesis([]classify.WindowSnapshot{}, tmpPath)
+	err := RunSynthesis([]classify.WindowSnapshot{}, tmpPath, synth.ClassFreqConfigs)
 	if err == nil {
 		t.Fatal("expected error for empty snapshot slice, got nil")
 	}
@@ -118,7 +118,7 @@ func TestZeroPacketError(t *testing.T) {
 		{Counts: map[classify.TrafficClass]int64{}, TotalPackets: 0, WindowIndex: 0},
 		{Counts: map[classify.TrafficClass]int64{}, TotalPackets: 0, WindowIndex: 1},
 	}
-	err2 := RunSynthesis(zeroSnaps, tmpPath2)
+	err2 := RunSynthesis(zeroSnaps, tmpPath2, synth.ClassFreqConfigs)
 	if err2 == nil {
 		t.Fatal("expected error for zero-packet snapshots, got nil")
 	}