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.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "moonset"
-version = "0.5.0"
+version = "0.6.0"
 edition = "2024"
 description = "Wayland session power menu with GTK4 and Layer Shell"
 license = "MIT"
@@ -17,7 +17,7 @@ serde = { version = "1", features = ["derive"] }
 nix = { version = "0.29", features = ["user"] }
 graphene-rs = { version = "0.22", package = "graphene-rs" }
 log = "0.4"
-env_logger = "0.11"
+systemd-journal-logger = "2.2"
 
 [dev-dependencies]
 tempfile = "3"