fix: cast mel to model dtype before VAE encode in DITTO reference loading

mel_converter outputs float32 (cuFFT requirement), but VAE encoder weights
are bfloat16. Cast mel to dtype before encode to avoid type mismatch.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

nodes/selva_ditto_optimizer.py

@@ -245,7 +245,7 @@ class SelvaDittoOptimizer:
                     if sr != sample_rate:
                         wav = torchaudio.functional.resample(wav, sr, sample_rate)
                     wav = wav.squeeze(0).to(device, torch.float32)
-                    mel = mel_converter(wav.unsqueeze(0))           # [1, n_mels, T_mel]
+                    mel = mel_converter(wav.unsqueeze(0)).to(dtype)  # [1, n_mels, T_mel]
                     # encode → sample → normalize (matches x at ODE endpoint)
                     z = feature_utils.tod.encode(mel)               # DiagonalGaussianDistribution
                     z_sample = z.sample().transpose(1, 2)           # [1, T_lat, C_lat]