fix: audit fixes — RefCell across await, async avatar decode (v0.6.10)

- init_fingerprint_async: hoist username before the await so a concurrent
  connect_monitor signal (hotplug / suspend-resume) cannot cause a RefCell
  panic. Re-borrow after the await for signal wiring.
- set_avatar_from_file: decode via gio::File::read_future +
  Pixbuf::from_stream_at_scale_future so the GTK main thread stays
  responsive during monitor hotplug. Default icon shown while loading.

src/lockscreen.rs

@@ -623,30 +623,41 @@ fn render_blurred_texture(
 }
 
 /// Load an image file and set it as the avatar. Stores the texture in the cache.
+/// Decoding runs via GIO async I/O + async pixbuf stream loader so the GTK main
+/// loop stays responsive — avatars may be loaded inside the `connect_monitor`
+/// signal handler at hotplug time, which must not block. The fallback icon is
+/// shown immediately; the decoded texture replaces it when ready.
 fn set_avatar_from_file(
     image: &gtk::Image,
     path: &Path,
     cache: &Rc<RefCell<Option<gdk::Texture>>>,
 ) {
-    let path_str = match path.to_str() {
-        Some(s) => s,
-        None => {
-            log::warn!("Avatar path is not valid UTF-8: {:?}", path);
-            image.set_icon_name(Some("avatar-default-symbolic"));
-            return;
+    image.set_icon_name(Some("avatar-default-symbolic"));
+
+    let display_path = path.to_path_buf();
+    let file = gio::File::for_path(path);
+    let image_clone = image.clone();
+    let cache_clone = cache.clone();
+
+    glib::spawn_future_local(async move {
+        let stream = match file.read_future(glib::Priority::default()).await {
+            Ok(s) => s,
+            Err(e) => {
+                log::warn!("Failed to open avatar {}: {e}", display_path.display());
+                return;
+            }
+        };
+        match Pixbuf::from_stream_at_scale_future(&stream, AVATAR_SIZE, AVATAR_SIZE, true).await {
+            Ok(pixbuf) => {
+                let texture = gdk::Texture::for_pixbuf(&pixbuf);
+                image_clone.set_paintable(Some(&texture));
+                *cache_clone.borrow_mut() = Some(texture);
+            }
+            Err(e) => {
+                log::warn!("Failed to decode avatar from {}: {e}", display_path.display());
+            }
         }
-    };
-    match Pixbuf::from_file_at_scale(path_str, AVATAR_SIZE, AVATAR_SIZE, true) {
-        Ok(pixbuf) => {
-            let texture = gdk::Texture::for_pixbuf(&pixbuf);
-            image.set_paintable(Some(&texture));
-            *cache.borrow_mut() = Some(texture);
-        }
-        Err(e) => {
-            log::warn!("Failed to load avatar from {:?}: {e}", path);
-            image.set_icon_name(Some("avatar-default-symbolic"));
-        }
-    }
+    });
 }
 
 /// Load the default avatar SVG from GResources, tinted with the foreground color.