feat(vk-messenger): add VK Messenger package

Repacks the official Electron build vk.me/app serves directly (no GitHub
release or distro repo for this product). Upstream's own .deb installs
under the literal Cyrillic product name /opt/VK Мессенджер — package()
resolves that directory dynamically instead of hardcoding it, then lays
the payload out under a clean /opt/vk-messenger to match this repo's
convention.

vk-messenger/postremove.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+set -euo pipefail
+
+optional_refresh() {
+    local label=$1
+    shift
+    if ! "$@"; then
+        echo "Предупреждение: не удалось обновить ${label}." >&2
+    fi
+}
+
+if command -v update-desktop-database >/dev/null 2>&1; then
+    optional_refresh "desktop-базу" update-desktop-database -q /usr/share/applications
+fi
+
+if command -v gtk-update-icon-cache >/dev/null 2>&1; then
+    optional_refresh "кэш иконок" gtk-update-icon-cache -f -q /usr/share/icons/hicolor
+fi
+
+if command -v kbuildsycoca6 >/dev/null 2>&1; then
+    optional_refresh "кэш KDE" kbuildsycoca6 --noincremental
+elif command -v kbuildsycoca5 >/dev/null 2>&1; then
+    optional_refresh "кэш KDE" kbuildsycoca5 --noincremental
+fi