fix(headless/kde): virtual Punktfunk speaker + restart host with the session

Audio: a headless host has no speakers, and on a LAN with AirPlay devices PipeWire picks a random
HomePod as default — so desktop audio (which the host captures from the default sink's monitor)
went to a HomePod over AirPlay instead of to the client, and there was no "Punktfunk" output to
select. Ship a `punktfunk-sink.conf` (a `support.null-audio-sink` adapter — NOT the non-existent
module-null-sink, which makes pipewire refuse to start) with high priority.session so it's the
default; run-headless-kde.sh installs it and restarts pipewire once on first install. The host then
captures its monitor and streams it. (Disable AirPlay sinks out of band: `dnf remove
pipewire-config-raop`.)

Input: the host's libei portal D-Bus connection goes stale when the compositor session restarts the
portal under it, and the in-process reopen loop can't recover it (EIS setup keeps timing out) — only
a full restart does. Add PartOf=punktfunk-kde-session.service so the host restarts with the session.

Both verified live on the Fedora 44 KDE box.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packaging/debian/build-deb.sh

@@ -48,6 +48,7 @@ sed -i 's#%h/punktfunk/target/release/punktfunk-host#/usr/bin/punktfunk-host#' \
 install -Dm0755 scripts/headless/run-headless-kde.sh   "$SHAREDIR/headless/run-headless-kde.sh"
 install -Dm0755 scripts/headless/run-headless-sway.sh  "$SHAREDIR/headless/run-headless-sway.sh"
 install -Dm0644 scripts/headless/kde-authorized        "$SHAREDIR/headless/kde-authorized"
+install -Dm0644 scripts/headless/punktfunk-sink.conf   "$SHAREDIR/headless/punktfunk-sink.conf"
 install -Dm0644 scripts/host.env.example           "$SHAREDIR/host.env.example"
 install -Dm0644 packaging/bazzite/host.env         "$SHAREDIR/host.env.bazzite"
 install -Dm0644 docs/api/openapi.json              "$SHAREDIR/openapi.json"