v1.3.1 security release

Security hardening release. All users should upgrade: pip install -U phantom-audio

Fixes

• Output writes are now always confined to a sandbox (default ~/.phantom/output, override with PHANTOM_OUTPUT_DIR). Closes an arbitrary file-write path in the default configuration.
• Decode-bomb guards added to the stem-separation and render paths (duration/size caps + ffmpeg -max_alloc/-t/-fs).
• Atomic, race-free output creation in reference matching; symlink TOCTOU hardening on confined input reads.

Behavior change

• Default output location moved from next to the input file to ~/.phantom/output. Set PHANTOM_OUTPUT_DIR to write elsewhere. Input reads stay unconfined unless PHANTOM_AUDIO_DIR is set.

See the published Security Advisory for full details and CVEs.