Linux desktop field verification

[t1ktakdev]

The core and CI run on Linux, but the desktop flow still needs a real-machine pass before Linux can be called tested.

Scope:

• run the app on a current Linux desktop with the documented Tauri prerequisites;
• exercise the deterministic demo from open → investigation → verification → explicit Apply;
• confirm the original fixture stays unchanged until Apply;
• check recovery after closing/reopening the app mid-investigation;
• record any platform-specific filesystem, process or WebKit issues;
• update docs/implementation-status.md with the exact environment and results.

Keep this evidence-based: note the distro, desktop/session, Rust/Node versions and the commands that were actually run.