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/users.rs

@@ -46,7 +46,10 @@ pub fn get_users(passwd_path: Option<&Path>) -> Vec<User> {
 
     let content = match fs::read_to_string(path) {
         Ok(c) => c,
-        Err(_) => return Vec::new(),
+        Err(e) => {
+            log::warn!("Failed to read passwd file {}: {e}", path.display());
+            return Vec::new();
+        }
     };
 
     let mut users = Vec::new();
@@ -88,6 +91,7 @@ pub fn get_users(passwd_path: Option<&Path>) -> Vec<User> {
         });
     }
 
+    log::debug!("Found {} login user(s)", users.len());
     users
 }
 
@@ -106,21 +110,28 @@ pub fn get_avatar_path_with(
     // AccountsService icon takes priority
     if accountsservice_dir.exists() {
         let icon = accountsservice_dir.join(username);
-        if let Ok(meta) = icon.symlink_metadata()
-            && !meta.file_type().is_symlink()
-        {
-            return Some(icon);
+        if let Ok(meta) = icon.symlink_metadata() {
+            if meta.file_type().is_symlink() {
+                log::warn!("Rejecting symlink avatar for {username}: {}", icon.display());
+            } else {
+                log::debug!("Avatar for {username}: AccountsService {}", icon.display());
+                return Some(icon);
+            }
         }
     }
 
     // ~/.face fallback
     let face = home.join(".face");
-    if let Ok(meta) = face.symlink_metadata()
-        && !meta.file_type().is_symlink()
-    {
-        return Some(face);
+    if let Ok(meta) = face.symlink_metadata() {
+        if meta.file_type().is_symlink() {
+            log::warn!("Rejecting symlink avatar for {username}: {}", face.display());
+        } else {
+            log::debug!("Avatar for {username}: ~/.face {}", face.display());
+            return Some(face);
+        }
     }
 
+    log::debug!("No avatar found for {username}");
     None
 }