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/sessions.rs

@@ -46,8 +46,17 @@ fn parse_desktop_file(path: &Path, session_type: &str) -> Option<Session> {
         }
     }
 
-    let name = name.filter(|s| !s.is_empty())?;
-    let exec_cmd = exec_cmd.filter(|s| !s.is_empty())?;
+    let name = name.filter(|s| !s.is_empty());
+    let exec_cmd = exec_cmd.filter(|s| !s.is_empty());
+
+    if name.is_none() || exec_cmd.is_none() {
+        log::debug!("Skipping {}: missing Name={} Exec={}", path.display(),
+            name.is_some(), exec_cmd.is_some());
+        return None;
+    }
+
+    let name = name?;
+    let exec_cmd = exec_cmd?;
 
     Some(Session {
         name,
@@ -74,7 +83,10 @@ pub fn get_sessions(
     for (dirs, session_type) in [(wayland, "wayland"), (xsession, "x11")] {
         for directory in dirs {
             let entries = match fs::read_dir(directory) {
-                Ok(e) => e,
+                Ok(e) => {
+                    log::debug!("Scanning session directory: {}", directory.display());
+                    e
+                }
                 Err(_) => continue,
             };
 
@@ -93,6 +105,7 @@ pub fn get_sessions(
         }
     }
 
+    log::debug!("Found {} session(s)", sessions.len());
     sessions
 }