packaging: split vgpu perception into separate libvgpu-perception0 + -dev packages

- the vmsig package no longer ships the gpu lib; it is a Sensor lib for the control, not the daemon
- vgpu-perception gets SOVERSION; runtime (libvgpu-perception0) and dev (-dev) packages, like the vmie split
- per-component install + a 3-package make deb; fix a stale comment (the windows producer is in-tree)

packaging/deb/vmsig/conffiles

@@ -0,0 +1 @@
+/etc/vmsig/vmsigd.conf

packaging/deb/vmsig/control.in

@@ -0,0 +1,13 @@
+Package: vmsig
+Version: @VERSION@
+Section: admin
+Priority: optional
+Architecture: amd64
+Depends: @DEPENDS@
+Maintainer: @MAINTAINER@
+Description: VM signaling coherence daemon
+ vmsig serves a unix-socket control plane over the signaling layer for the VMs it
+ discovers: lifecycle/state, coherent guest address-space context handoff, and arbitrated
+ input and memory-write actuation. Ships the daemon (vmsigd), the signaling library, and a
+ systemd unit. Configured via /etc/vmsig/vmsigd.conf. The host-side vgpu perception library
+ is a separate package (libvgpu-perception).

packaging/deb/vmsig/postinst

@@ -0,0 +1,19 @@
+#!/bin/sh
+set -e
+case "$1" in
+configure)
+    ldconfig || true
+    mkdir -p /etc/vmsig
+    chmod 0640 /etc/vmsig/vmsigd.conf 2>/dev/null || true   # carries the uid->grant policy
+    mkdir -p /dev/shm/vmsig && chmod 0755 /dev/shm/vmsig     # also (re)created at boot via tmpfiles
+    if [ -d /run/systemd/system ]; then
+        systemctl daemon-reload || true
+        systemd-tmpfiles --create /usr/lib/tmpfiles.d/vmsig.conf || true
+        systemctl enable vmsigd.service || true              # enable, but do NOT start
+    fi
+    echo "vmsig: review the [grant] policy in /etc/vmsig/vmsigd.conf, then: systemctl start vmsigd" >&2
+    ;;
+abort-upgrade|abort-remove|abort-deconfigure)
+    ;;
+esac
+exit 0

packaging/deb/vmsig/prerm

@@ -0,0 +1,12 @@
+#!/bin/sh
+set -e
+case "$1" in
+remove|deconfigure)
+    if [ -d /run/systemd/system ]; then
+        systemctl disable --now vmsigd.service || true
+    fi
+    ;;
+upgrade|failed-upgrade)
+    ;;
+esac
+exit 0