fix: packages.conf format, add init icons, instant wallpaper

- packages.conf: fix operations format (strings -> empty list)
- netinstall.yaml: remove empty Style group
- packagechooser.conf: add Breeze-style init system SVG icons
- wallpaper: pre-bake config in skel for instant wallpaper, remove wait loop
- AGENTS.md: add GPG signing instructions

iso-profiles/antergos/live-overlay/etc/calamares/modules/packages.conf

@@ -1,6 +1,13 @@
+---
 backend: pacman
-operations:
-  - install
-  - remove
-  - update
+skip_if_no_internet: false
 update_db: true
+ignore_update_db_error: false
+update_system: false
+
+pacman:
+    num_retries: 3
+    disable_download_timeout: false
+    needed_only: true
+
+operations: []