v0.4.0: branding refresh, breadpaper baked in, bos-settings 0.4.0

- Move assets to assets/ directory (bread_white.svg, icons 256/512/1024px)
- Update Calamares branding + Plymouth theme logos
- Bake breadpaper (wallpaper manager + pywal) into /etc/skel alongside the
  rest of the bread ecosystem — previously missing from the ISO build
- Bump bos-settings to 0.4.0

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FHr5CeufsAfTrt41XoApir

Cargo.lock

@@ -28,7 +28,7 @@ checksum = "b4388bee8683e3d04af747c73422af53102d2bd24d9eadb6cbc100baef4b43f8"
 
 [[package]]
 name = "bos-settings"
-version = "0.3.1"
+version = "0.4.0"
 dependencies = [
  "async-channel",
  "bread-theme",