feat: switch to systemd-journal-logger, add debug logging (v0.6.0)

Replace env_logger with systemd-journal-logger for consistent logging
across moonset/moonlock/moongreet. Add MOONSET_DEBUG env var and debug
statements across all modules. Also includes shared blur cache for
multi-monitor and detached moonlock spawn for lock action.

CHANGELOG.md

@@ -3,6 +3,19 @@
 All notable changes to this project will be documented in this file.
 Format based on [Keep a Changelog](https://keepachangelog.com/).
 
+## [0.6.0] - 2026-03-28
+
+### Added
+
+- Systemd journal logging (`journalctl -t moonset`) replacing env_logger stderr output
+- `MOONSET_DEBUG` env var to enable debug-level journal output
+- Debug logging across all modules (config resolution, wallpaper source, avatar loading, power actions, locale detection, blur cache)
+- Shared blur cache for multi-monitor — GPU blur computed once, reused by all windows
+
+### Changed
+
+- Lock action spawns moonlock as detached process instead of blocking via run_command — moonset can quit immediately while moonlock runs independently
+
 ## [0.4.1] - 2026-03-28
 
 ### Added