fix(09-01): add TestGroupFieldPopulated, fix oscillator normalization, update tests

- Add TestGroupFieldPopulated test to verify all ClassFreqConfigs have non-empty Group (GRP-01)
- Change TestHarmonicsNonEmpty threshold from < 2 to < 1 (accepts single-harmonic sine entries)
- Fix oscillator Advance() to use math.Abs(h.Amplitude) for normalization weight accumulation:
  triangle wave uses alternating-sign amplitudes; signed sum underestimates totalWeight causing
  output to exceed [-1,1] bounds when using WaveformPresetHarmonics (Rule 1 bug fix)
- Update TestStereoPan to use ClassSSH (pan=-0.7) instead of ClassDHCP (pan changed to 0.1)
- Update TestNewBankCustomConfigNoClip: passes after oscillator normalization fix
- Fix TestLoadPartialOverrideFrequency: derive expected WaveformType from defaults (not hardcoded 0)
- Fix TestAutoFreqSkipsBuiltins: derive expected HTTPS BaseHz from defaults (150.0 in Phase 9)

synth/bank_test.go

@@ -104,8 +104,8 @@ func TestMixerNoClip(t *testing.T) {
 func TestStereoPan(t *testing.T) {
 	b := NewBank(0.01, ClassFreqConfigs) // fast EMA
 	counts := make(map[classify.TrafficClass]int64)
-	// ClassDHCP has pan=-0.75 (wide-left in config.go)
-	counts[classify.ClassDHCP] = 1000
+	// ClassSSH has pan=-0.7 (wide-left in Phase 9 config.go)
+	counts[classify.ClassSSH] = 1000
 	snap := classify.WindowSnapshot{
 		Counts:       counts,
 		TotalPackets: 1000,
@@ -125,7 +125,7 @@ func TestStereoPan(t *testing.T) {
 	rmsL := math.Sqrt(sumL2 / float64(len(frames)))
 	rmsR := math.Sqrt(sumR2 / float64(len(frames)))
 	if rmsL <= rmsR {
-		t.Errorf("ClassDHCP (pan=-0.75) should have rmsL > rmsR; got rmsL=%v, rmsR=%v", rmsL, rmsR)
+		t.Errorf("ClassSSH (pan=-0.7) should have rmsL > rmsR; got rmsL=%v, rmsR=%v", rmsL, rmsR)
 	}
 }