feat: bake packagechooserq module into the ISO, fix Steamify page styling

packagechooserq is excluded from cachyos-calamares-next's own build, so its
.so + module.desc are added straight into airootfs (matching the module
built against the current cachyos-calamares-next). Also:

- SteamifyPage.qml: border-only row highlight (was a translucent teal fill
  that made white text unreadable), themed page background (was falling
  through to Calamares' default white), a sub-option "└" marker, more right
  padding so the row border clears the scrollbar.
- calamares-online.sh: also write items.json next to Items.qml, so
  packagechooserq's prettyStatus() can show the Summary step's choice as
  labels instead of raw, comma-joined ids.

archiso/airootfs/usr/lib/calamares/modules/packagechooserq/module.desc

@@ -0,0 +1,7 @@
+# AUTO-GENERATED metadata file
+# Syntax is YAML 1.2
+---
+type: "viewmodule"
+name: "packagechooserq"
+interface: "qtplugin"
+load: "libcalamares_viewmodule_packagechooserq.so"