feat: switch to systemd-journal-logger, add debug logging (v0.4.0)

Replace env_logger file-based logging with systemd-journal-logger for
consistency with moonlock and native journalctl integration. Add debug-level
logging at all decision points: config loading, user/session detection,
avatar resolution, locale detection, IPC messages, login flow, and
persistence. No credentials are ever logged.

src/main.rs

@@ -13,8 +13,6 @@ use gdk4 as gdk;
 use gtk4::prelude::*;
 use gtk4::{self as gtk, gio};
 use gtk4_layer_shell::LayerShell;
-use std::path::PathBuf;
-
 fn load_css(display: &gdk::Display) {
     let css_provider = gtk::CssProvider::new();
     css_provider.load_from_resource("/dev/moonarch/moongreet/style.css");
@@ -48,13 +46,16 @@ fn activate(app: &gtk::Application) {
         }
     };
 
+    log::debug!("Display: {:?}", display);
     load_css(&display);
 
     // Load config and resolve wallpaper
     let config = config::load_config(None);
     let bg_path = config::resolve_background_path(&config);
+    log::debug!("Background path: {}", bg_path.display());
 
     let use_layer_shell = std::env::var("MOONGREET_NO_LAYER_SHELL").is_err();
+    log::debug!("Layer shell: {use_layer_shell}");
 
     // Main greeter window (login UI) — compositor picks focused monitor
     let greeter_window = greeter::create_greeter_window(&bg_path, &config, app);
@@ -66,6 +67,7 @@ fn activate(app: &gtk::Application) {
     // Wallpaper-only windows on all monitors (only with layer shell)
     if use_layer_shell {
         let monitors = display.monitors();
+        log::debug!("Monitor count: {}", monitors.n_items());
         for i in 0..monitors.n_items() {
             if let Some(monitor) = monitors
                 .item(i)
@@ -81,25 +83,11 @@ fn activate(app: &gtk::Application) {
 }
 
 fn setup_logging() {
-    let mut builder = env_logger::Builder::from_default_env();
-    builder.filter_level(log::LevelFilter::Info);
-
-    // Try file logging to /var/cache/moongreet/ — fall back to stderr
-    let log_dir = PathBuf::from("/var/cache/moongreet");
-    if log_dir.is_dir() {
-        let log_file = log_dir.join("moongreet.log");
-        use std::os::unix::fs::OpenOptionsExt;
-        if let Ok(file) = std::fs::OpenOptions::new()
-            .create(true)
-            .append(true)
-            .mode(0o640)
-            .open(&log_file)
-        {
-            builder.target(env_logger::Target::Pipe(Box::new(file)));
-        }
-    }
-
-    builder.init();
+    systemd_journal_logger::JournalLog::new()
+        .unwrap()
+        .install()
+        .unwrap();
+    log::set_max_level(log::LevelFilter::Debug);
 }
 
 fn main() {