SA3 VAE bf16 corruption - repro evidence

Evidence assets for the Stable Audio 3 VAE bf16-on-MPS fix (branch fix-sa3-audio-vae-bf16-mps). Before/after audio decoded from the same fixed-seed latent, spectrograms, the pinned latent, a standalone A/B repro script, and the generating workflow. Kept as release assets so no generated media enters git history.