"""Audio Decoder module.

Responsibility: convert audio files into normalized DecodedAudio objects.

Capabilities (per SPEC.md §23.2):
- Decode WAV, FLAC, AIFF, AIF
- Normalize to float32 [-1.0, 1.0]
- Preserve original sample rate
- Preserve channel count (no downmixing)
- Extract technical metadata (duration, sample_rate, channels, bit_depth)

Output: DecodedAudio

This module must NOT calculate DSP, calculate embeddings, or access
the database.
"""