R.I.P. Cnchi (2012-2026) — switch to Calamares as sole installer

Cnchi was the heart of Antergos, but the GTK4 Python port proved
too unstable and maintenance-heavy for a solo dev to carry.
GTK4 Python bindings broke on every upstream release, the
codebase was brittle, and maintaining it consumed time that
should go into actual improvements.

Calamares is now the sole installer. It's mature, upstream-
supported, modular C++/Qt6, and with our branding package
it supports:
  - Offline mode (GNOME squashfs, no internet needed)
  - Online mode (8 DEs via netinstall)
  - dracut initramfs
  - zenity/kdialog launcher (calamares-next)

What changed:
  - packages/cnchi/ deleted entirely
  - packages.yaml: cnchi removed, memes kept
  - antergos-next-memes: repurposed from 'Cnchi audio enhancements'
    to generic 'Antergos NeXT welcome audio', path changed from
    /usr/share/cnchi-memes/ to /usr/share/antergos-next-memes/
  - calamares-branding show.qml: Cnchi line → Calamares line
  - README: Cnchi table → HAL section, sources updated

The welcome app's startup jingle still works — the memes package
lives on, just without the Cnchi association.

packages/calamares-branding-antergos-next/show.qml

@@ -145,7 +145,7 @@ Presentation
 
                 Text { text: "• Welcome app — system info & quick config" ; font.pixelSize: 13 ; color: "#34495E" }
                 Text { text: "• Calamares installer — easy setup" ; font.pixelSize: 13 ; color: "#34495E" }
-                Text { text: "• Cnchi — classic Antergos installer" ; font.pixelSize: 13 ; color: "#34495E" }
+                Text { text: "• Calamares — easy setup with offline & online modes" ; font.pixelSize: 13 ; color: "#34495E" }
                 Text { text: "• Pacman + AUR helper — full package access" ; font.pixelSize: 13 ; color: "#34495E" }
                 Text { text: "• Online documentation and community" ; font.pixelSize: 13 ; color: "#34495E" }
             }