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/local/bin/calamares-online.sh

@@ -73,6 +73,9 @@ EOF
           cat "$tmp"
           printf '\n}\n'
         } | sudo tee "$sqml/Items.qml" > /dev/null
+        # Same rows, plain JSON: packagechooserq's prettyStatus() override
+        # reads this to show the Summary step's choice as labels, not ids.
+        sudo cp "$tmp" "$sqml/items.json"
     fi
     rm -f "$tmp"