fix: automatic disk cleanup on upload and document deletion

[sharadcodes]

Summary

Fixes a disk space leak where uploaded source files and generated audio files were left on disk after document deletion.

Changes

Upload Temporary File Cleanup

• Wraps the upload processing in a try/finally block
• Immediately deletes the original uploaded file (.epub/.txt) and any intermediate Calibre-extracted .extracted.txt file from /data/uploads/ after text import
• If the import fails at any stage, also cleans up the cover image target to prevent orphan files

Document Deletion Disk Cleanup

• delete_document now accepts Settings and queries all associated Job IDs before deleting DB rows
• After DB deletion, unlinks the cover image file from /data/uploads/
• Recursively deletes the generated audio directory /data/audio/<job_id>/ for all associated jobs (MP3, WAV chunks)

Tests

Added tests/test_api_cleanup.py with an integration test that verifies:

1. After upload: temporary source file is deleted, only cover image remains in /data/uploads/
2. After document delete: cover image is unlinked, all generated job audio directories are removed from disk

All 48 tests pass. ✅