feat: switch logging to systemd journal (v0.4.2)

Replace env_logger + /var/cache/moonlock file logging with
systemd-journal-logger. Logs are now reliably accessible via
journalctl --user -u moonlock, fixing invisible errors in the
systemd user service context.

- Cargo.toml: env_logger → systemd-journal-logger 2.2
- main.rs: setup_logging() uses JournalLog
- PKGBUILD: add systemd-libs dependency
- power.rs: include unstaged systemctl fixes (ABOUTME, --no-ask-password, output())

CLAUDE.md

@@ -40,11 +40,11 @@ LD_PRELOAD=/usr/lib/libgtk4-layer-shell.so ./target/release/moonlock
 - `auth.rs` — PAM-Authentifizierung via Raw FFI (unsafe extern "C" conv callback, msg_style-aware, Zeroizing<Vec<u8>>)
 - `fingerprint.rs` — fprintd D-Bus Listener (Rc<RefCell<FingerprintListener>>, self-wiring g-signal via connect_local)
 - `users.rs` — Aktuellen User via nix getuid, Avatar-Loading mit Symlink-Rejection
-- `power.rs` — Reboot/Shutdown via /usr/bin/loginctl
+- `power.rs` — Reboot/Shutdown via /usr/bin/systemctl
 - `i18n.rs` — Locale-Erkennung und String-Tabellen (DE/EN), faillock_warning mit konfigurierbarem max_attempts
 - `config.rs` — TOML-Config (background_path, fingerprint_enabled als Option<bool>) + Wallpaper-Fallback
 - `lockscreen.rs` — GTK4 UI, PAM-Auth via gio::spawn_blocking, Fingerprint-Indikator, Zeroizing<String> für Passwort, Power-Confirm
-- `main.rs` — Entry Point, Panic-Hook, Root-Check, ext-session-lock-v1 (Pflicht in Release), Multi-Monitor
+- `main.rs` — Entry Point, Panic-Hook, Root-Check, ext-session-lock-v1 (Pflicht in Release), Multi-Monitor, systemd-Journal-Logging
 
 ## Sicherheit