feat(03-01): extend TrafficClass to 14 classes with hash-bucketed unknowns

- Replace ClassUnknown with ClassUnknown1-4 (unknown-1 through unknown-4)
- AllClasses() now returns 14 elements
- Add hashBucket() function routing unrecognized traffic deterministically
- Update synth/config.go: NumLayers=14, 4 dissonant unknown tone configs at 862-1047 Hz
- Add TestAllClassesCount and TestHashBucketDistribution tests
- Add TestClassFreqConfigsComplete and TestNumLayersMatchesAllClasses to config_test.go
- Update TestNewBankHas14Layers, TestMixerNoClip for 14 classes
- All classify and synth tests pass

synth/config_test.go

@@ -17,8 +17,9 @@ func TestAllClassesHaveConfig(t *testing.T) {
 
 func TestFrequenciesInRange(t *testing.T) {
 	for class, cfg := range synth.ClassFreqConfigs {
-		if cfg.BaseHz < 60 || cfg.BaseHz > 800 {
-			t.Errorf("class %q BaseHz=%.1f is out of range [60, 800]", class, cfg.BaseHz)
+		// D-05: unknown buckets use 850-1100 Hz dissonant range; known classes use 60-800 Hz
+		if cfg.BaseHz < 60 || cfg.BaseHz > 1100 {
+			t.Errorf("class %q BaseHz=%.1f is out of range [60, 1100]", class, cfg.BaseHz)
 		}
 	}
 }
@@ -48,3 +49,17 @@ func TestPanPositionsInRange(t *testing.T) {
 		}
 	}
 }
+
+func TestClassFreqConfigsComplete(t *testing.T) {
+	for _, class := range classify.AllClasses() {
+		if _, ok := synth.ClassFreqConfigs[class]; !ok {
+			t.Errorf("ClassFreqConfigs missing entry for class %q", class)
+		}
+	}
+}
+
+func TestNumLayersMatchesAllClasses(t *testing.T) {
+	if synth.NumLayers != len(classify.AllClasses()) {
+		t.Errorf("NumLayers=%d but AllClasses() has %d entries", synth.NumLayers, len(classify.AllClasses()))
+	}
+}