Sentinel v0.13.0

Sentinel 0.13.0

KDE-only. Sentinel now ships a single frontend — the KDE Plasma helper —
and the COSMIC frontend has been removed.

This is a packaging/structure change. The shared authentication backend
(PAM module, polkit agent, privilege-separation broker) is unchanged, and
there is no change to configuration or the auth path.

Removed

• The COSMIC frontend (sentinel-helper, libcosmic) and its locale
  bundles.
• The COSMIC root install.sh / uninstall.sh — the KDE installer at
  packaging-kde/install.sh is now the only installer.
• The sentinel-cosmic Arch/AUR package and the build-cosmic /
  publish-aur-cosmic release jobs.
• The entire libcosmic dependency tree, along with its deny.toml and
  cargo audit advisory/license carve-outs.

Unchanged

• The KDE helper (sentinel-helper-kde) and its AUR package
  (sentinel-kde) keep their names — existing users are unaffected.
• The PAM module, polkit agent, and broker — and all 0.12.0 behavior
  (per-command remember, sudo credential-cache control, the broker, …).

For users

• KDE users: nothing to do. sentinel-kde continues as before.
• COSMIC users: sentinel-cosmic is discontinued; its last release is
  0.12.0.

For packagers

• Build the helper with cargo build -p sentinel-helper-kde; the auth-path
  backend (pam-sentinel, sentinel-polkit-agent, sentinel-broker)
  builds with a bare cargo build.