Release v0.9.0-alpha

BREAKING CHANGES

• Switch encryption format to streaming AES-GCM with per-chunk nonces; existing data from previous versions cannot be decrypted

Added

• Implement safe backup write by writing to a temporary file and atomically
  replacing the final archive to avoid TOCTOU issues and partial files.
• Introduce a cross-process lock via a .lock file and atomic write of
  metadata.json to prevent corruption during concurrent updates.

Changed

• Migrated to src layout from flat layout.
• Updated dependencies:

Updated annotated-doc v0.0.4 -> v0.0.5
Updated cffi v2.0.0 -> v2.1.1
Removed click v8.3.3
Updated coverage v7.13.5 -> v7.15.4
Updated cryptography v47.0.0 -> v50.0.0
Updated hypothesis v6.152.4 -> v6.165.10
Updated markdown-it-py v4.0.0 -> v4.2.0
Updated packaging v26.2 -> v26.3
Updated pygments v2.20.0 -> v2.21.0
Updated pytest v9.0.3 -> v9.1.1
Updated ruff v0.15.12 -> v0.16.4
Updated typer v0.25.1 -> v0.27.1
Updated typing-extensions v4.15.0 -> v4.16.0

Fixed

• Skip unrecognised filenames when pruning