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>

scripts/70-punktfunk-client.rules

@@ -0,0 +1,12 @@
+# punktfunk-client: hidraw access for the seated user's DualSense (SDL's HIDAPI driver
+# needs it for touchpad / motion / lightbar / player LEDs / adaptive triggers — without it
+# SDL silently degrades to plain evdev, which has none of those). evdev joystick nodes are
+# already uaccess-tagged by systemd; hidraw nodes are root-only by default and systemd
+# declined a generic gamepad hwdb (systemd#22681), so we ship the rule, steam-devices
+# style: the ATTRS match covers USB, the KERNELS match covers Bluetooth.
+# DualSense (054c:0ce6)
+KERNEL=="hidraw*", ATTRS{idVendor}=="054c", ATTRS{idProduct}=="0ce6", MODE="0660", TAG+="uaccess"
+KERNEL=="hidraw*", KERNELS=="*054C:0CE6*", MODE="0660", TAG+="uaccess"
+# DualSense Edge (054c:0df2)
+KERNEL=="hidraw*", ATTRS{idVendor}=="054c", ATTRS{idProduct}=="0df2", MODE="0660", TAG+="uaccess"
+KERNEL=="hidraw*", KERNELS=="*054C:0DF2*", MODE="0660", TAG+="uaccess"