Package Effector for Arch and give it a desktop entry

packaging/arch/PKGBUILD builds the tagged release from this repository
and installs it with pacman; the version test keeps its pkgver in step
with CMakeLists.txt. A desktop entry puts the interface in the app menu.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/arch/PKGBUILD

@@ -0,0 +1,30 @@
+# Builds the release tagged v$pkgver from the repository this file sits in,
+# so pkgver must follow the project() line of CMakeLists.txt (the version core
+# test checks it). From this folder: makepkg -si
+pkgname=effector
+pkgver=0.5.1
+pkgrel=1
+pkgdesc='Image effects app: a GTK4 interface and a headless CLI over pluggable effects'
+arch=('x86_64' 'aarch64')
+url='https://git.plan9.uber.space/hans/effector'
+license=('unknown')
+depends=('gtkmm-4.0' 'gdk-pixbuf2' 'pango' 'cairo' 'glib2' 'glibc' 'gcc-libs')
+makedepends=('cmake' 'ninja' 'git')
+checkdepends=('xorg-server-xvfb')
+source=("$pkgname::git+file://${startdir%/packaging/arch}#tag=v$pkgver")
+sha256sums=('SKIP')
+
+build() {
+    cmake -S "$pkgname" -B build -G Ninja \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX=/usr
+    cmake --build build
+}
+
+check() {
+    ctest --test-dir build --output-on-failure
+}
+
+package() {
+    DESTDIR="$pkgdir" cmake --install build
+}