fix(packaging): autoload vhci-hcd and open its attach files for the usbip Deck pad

Steam Input only adopts the virtual Steam Deck controller when it arrives as
a real USB device (raw_gadget or usbip/vhci transports); the UHID fallback
has no USB interface and Steam ignores it. On a stock host neither
precondition for usbip held: vhci-hcd isn't loaded, and its sysfs
attach/detach files are root-only while the host runs as a user service —
so every session silently fell back to UHID and 'no controller appears on
the host' (live-debugged 2026-07-08: client events all arrived, the pad
existed, Steam just refused it).

Ship both preconditions with the host packages:
 * modules-load.d/punktfunk.conf loads vhci-hcd at boot (rpm/deb/arch;
   Bazzite gets it via the RPM payload + a modprobe in the sysext
   post-merge hook)
 * a udev rule in 60-punktfunk.rules grants the input group write on
   vhci_hcd's attach/detach whenever the device appears

Verified end-to-end on a live host: usbip in-process attach, hid-steam
binds all three interfaces, 'Steam Deck' + motion evdev appear, and Steam
adopts the pad (client-mode grab + its own virtual X360 emission).

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

packaging/bazzite/punktfunk-sysext.sh

@@ -77,6 +77,10 @@ post_merge() {
   for f in /usr/lib/sysctl.d/99-punktfunk-net.conf /usr/lib/sysctl.d/99-punktfunk-client-net.conf; do
     [ -f "$f" ] && sysctl -q -p "$f" 2>/dev/null || :
   done
+  # vhci-hcd now, no reboot (modules-load.d/punktfunk.conf covers boot): the usbip transport
+  # that makes the virtual Steam Deck pad a real USB device Steam Input adopts. The udev add
+  # event fires the 60-punktfunk.rules vhci rule, opening the attach files to the input group.
+  [ -f /usr/lib/modules-load.d/punktfunk.conf ] && modprobe vhci-hcd 2>/dev/null || :
   # The /etc payload a sysext can't carry. The gamescope-session drop-in is %config(noreplace):
   # only seed it, never clobber a local edit. The tray autostart entry is not user config.
   if [ -f "$ETC_SRC/gamescope-session-plus/sessions.d/steam" ] \