fix: elevate CSS priority to override GTK4 user theme (v0.6.1)

Colloid-Catppuccin theme loaded via ~/.config/gtk-4.0/gtk.css at
PRIORITY_USER (800) was overriding moongreet's PRIORITY_APPLICATION (600),
causing avatar to lose its circular border-radius.

- Use STYLE_PROVIDER_PRIORITY_USER for app CSS provider
- Replace border-radius: 50% with 9999px (GTK4 CSS percentage quirk)
- Include missed Cargo.lock and PKGBUILD updates from v0.6.0

Cargo.lock

@@ -569,7 +569,7 @@ dependencies = [
 
 [[package]]
 name = "moongreet"
-version = "0.5.3"
+version = "0.6.1"
 dependencies = [
  "gdk-pixbuf",
  "gdk4",