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.go

@@ -41,9 +41,10 @@ func EncodeMP3(outputPath string, frames [][2]float64, sampleRate int) error {
 
 // RunSynthesis consumes a slice of WindowSnapshots, renders audio via OscillatorBank,
 // and encodes to MP3 at outputPath.
+// freqCfgs is the merged config map from config.Load (D-10: injected, not hardcoded).
 // Returns an error if zero packets were captured (D-16 / OUT-03).
 // The zero-packet guard runs BEFORE file creation to avoid leaving an empty file on disk.
-func RunSynthesis(snapshots []classify.WindowSnapshot, outputPath string) error {
+func RunSynthesis(snapshots []classify.WindowSnapshot, outputPath string, freqCfgs map[classify.TrafficClass]synth.FreqConfig) error {
 	// D-16 / OUT-03: Zero-packet guard — check BEFORE creating output file
 	var totalPackets int64
 	for _, snap := range snapshots {
@@ -54,7 +55,7 @@ func RunSynthesis(snapshots []classify.WindowSnapshot, outputPath string) error
 	}
 
 	// Render all windows to stereo frames
-	bank := synth.NewBank(1.0, synth.ClassFreqConfigs) // tau=1.0s per D-07
+	bank := synth.NewBank(1.0, freqCfgs) // tau=1.0s per D-07
 	var allFrames [][2]float64
 	for _, snap := range snapshots {
 		frames := bank.RenderWindow(snap)