fix: audit LOW fixes — dead uid, home_dir warn, clippy sweep, debug value (v0.8.5)

- users::User: drop the unused `uid` field and its getuid() assignment.
  The compiler dead_code warning is gone, and the synthetic `u32::MAX`
  sentinel in the panel fallback is obsolete too.
- panel: surface a log::warn! when dirs::home_dir() returns None instead
  of silently falling back to an empty PathBuf that would make avatars
  look for .face in the current working directory.
- Apply three clippy suggestions: two collapsible if-let + && chains in
  users::get_avatar_path_with and config::resolve_background_path_with,
  and a redundant closure in panel::execute_action's spawn_blocking.
- main: require MOONSET_DEBUG=1 to escalate log verbosity — mere
  presence of the var must not dump path info into the journal.

src/users.rs

@@ -12,7 +12,6 @@ pub struct User {
     pub username: String,
     pub display_name: String,
     pub home: PathBuf,
-    pub uid: u32,
 }
 
 /// Get the currently logged-in user's info from the system.
@@ -37,7 +36,6 @@ pub fn get_current_user() -> Option<User> {
         username: nix_user.name,
         display_name,
         home: nix_user.dir,
-        uid: uid.as_raw(),
     })
 }
 
@@ -65,16 +63,16 @@ pub fn get_avatar_path_with(
     }
 
     // AccountsService icon fallback
-    if let Some(name) = username {
-        if accountsservice_dir.exists() {
-            let icon = accountsservice_dir.join(name);
-            if let Ok(meta) = icon.symlink_metadata() {
-                if meta.file_type().is_symlink() {
-                    log::warn!("Rejecting symlink avatar: {}", icon.display());
-                } else if meta.is_file() {
-                    log::debug!("Avatar: using AccountsService icon ({})", icon.display());
-                    return Some(icon);
-                }
+    if let Some(name) = username
+        && accountsservice_dir.exists()
+    {
+        let icon = accountsservice_dir.join(name);
+        if let Ok(meta) = icon.symlink_metadata() {
+            if meta.file_type().is_symlink() {
+                log::warn!("Rejecting symlink avatar: {}", icon.display());
+            } else if meta.is_file() {
+                log::debug!("Avatar: using AccountsService icon ({})", icon.display());
+                return Some(icon);
             }
         }
     }