Harden audio conversion, editing, lifecycle, and product quality

[bigbruno]

Scope

Remediation of the technical and product audit of 95f02c3a019af7cb40813fa38af25c7b3906c99c (BAC-001 through BAC-034).

This draft is under active implementation. The initial commit establishes native Linux validation and prevents audit-branch pushes from triggering translation or package publication. Application fixes, regression tests, and an explicit finding-by-finding status will be added to this branch.

Validation policy

• Preserve the exact source revision and test evidence.
• Test real FFmpeg/ffprobe output, not only mocked command construction.
• Distinguish locally executed tests, CI results, and checks that require a real desktop/audio session.
• Do not claim that an audit finding is resolved until the corresponding change and evidence exist.
• Do not change the project's license without maintainer confirmation.

No changes are made directly to main. All code, comments, commit messages, and pull request documentation in this change set are written in English.