CLI recordings list misses Desktop's custom storage folders #2942

Description

cap recordings list --json misses recordings saved in Desktop's custom storage folder. Desktop shows them, and cap recordings list --dir /path/to/custom --json finds them, but the default CLI command only scans so.cap.desktop/recordings.

This also omits recordings in previously used storage folders that Desktop still includes in its library. Scripts using the default command get an incomplete library or [].

Reproduction

1. In Desktop settings, choose a custom recording storage folder.
2. Save a recording there and confirm it appears in Desktop's library.
3. Run cap recordings list --json.
4. Compare with cap recordings list --dir /path/to/custom --json.

Expected: the default command discovers the same storage roots as Desktop, while explicit --dir lists only the requested folder.

Actual: the default command misses the custom recording. Explicit --dir finds it.

Additional Context

• Source baseline: 1965b31796db6da107a8f859ff34397468ae9512.
• Reproduced on Linux by executing the unchanged production listing module and actual cap-project parser with isolated application data, Desktop's persisted settings, and a generated MP4 recording. No user recordings or settings were used.
• With one recording in custom storage and none in default storage, the baseline returned []. Passing the custom directory returned the recording with outputExists: true.
• Desktop already discovers current, default, and previous recording roots. The CLI's default_library_dir does not read those settings.
• Full native CLI build validation was blocked locally by a missing FFmpeg header, libavcodec/avfft.h. The reproduction used the actual production listing source in a small executable, rather than a separately implemented scanner.