ci(packaging): punktfunk-client .deb + RPM subpackage

Hook the Linux client into the existing packaging CI:

- deb.yml builds both binaries and publishes punktfunk-host AND
  punktfunk-client to the Gitea apt registry; new
  packaging/debian/build-client-deb.sh mirrors the host script
  (shlibdeps auto-Depends — GTK4/libadwaita/SDL3/FFmpeg/PipeWire
  sonames; no NVIDIA filter, the client links no CUDA). Built and
  inspected locally on Ubuntu 26.04.
- punktfunk.spec gains a "client" subpackage (binary + desktop entry +
  udev rule); rpm.yml's publish loop picks it up unchanged.
- New shared assets: packaging/linux/io.unom.Punktfunk.desktop and
  scripts/70-punktfunk-client.rules — DualSense hidraw uaccess (USB +
  Bluetooth, steam-devices style) so SDL's HIDAPI driver gets
  touchpad/motion/lightbar/triggers instead of degrading to evdev.
- Builder images learn the client link deps (rust-ci already had
  them; fedora-rpm adds gtk4/libadwaita/SDL3-devel) with idempotent
  install steps in deb.yml/rpm.yml since jobs run against the
  previous push's image.

Workspace check CI (build/clippy/test) already covers the crate since
f09def4.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packaging/linux/io.unom.Punktfunk.desktop

@@ -0,0 +1,10 @@
+[Desktop Entry]
+Type=Application
+Name=Punktfunk
+Comment=Stream a remote punktfunk host
+Exec=punktfunk-client
+Icon=video-display
+Terminal=false
+Categories=Network;Game;
+Keywords=streaming;remote;game;moonlight;
+StartupNotify=true