Spynel v0.12.16

Fixes autostart registration and new-workspace onboarding.

• Keep failed autostart changes from saving settings and restore prior registration after native failures.

• Require a reachable systemd manager before inspecting or changing Linux autostart.

• Show the standard welcome screen for newly created TUI conversations.

• Include the Codex model and speed selection fixes from the previously incomplete release.

• Use synthetic identity fixtures and remove local build paths from Linux release executables.