Add Arch Linux PKGBUILD and package build step

- PKGBUILD: builds converge package, uses pre-built binary from
  build/converge when available (from scripts/build), falls back to
  stack build from source. Installs binary, systemd user service,
  example config, and README.
- scripts/build: added final step to run makepkg -f on the host
  (conditional, skipped if makepkg not found). Produces .pkg.tar.zst
  alongside the binary.
- scripts/makepkg: convenience wrapper for standalone makepkg runs.

PKGBUILD

@@ -0,0 +1,67 @@
+# Maintainer: James Brechtel <james@flipstone.com>
+# Contributor: James Brechtel <james@flipstone.com>
+
+pkgname=converge
+_pkgver=0.1.0.0
+pkgver=${_pkgver//-/_}
+pkgrel=1
+pkgdesc="Auto-sync git repositories by watching for changes, committing, pulling, and pushing"
+arch=('x86_64')
+url="https://github.com/jbrechtel/converge"
+license=('BSD')
+makedepends=('stack' 'git')
+depends=('git' 'libnotify' 'gcc-libs')
+optdepends=('converge-relay: realtime push notifications via SSE relay server')
+backup=('etc/converge/config.example.yaml')
+source=(
+    "converge.service"
+    "converge.example.yaml"
+)
+md5sums=(
+    'SKIP'
+    'SKIP'
+)
+
+build() {
+    cd "$startdir"
+
+    # Use pre-built binary if available (e.g. from scripts/build), otherwise build from source
+    if [[ -x build/converge ]]; then
+        msg "Using pre-built binary from build/converge"
+        install -Dm755 build/converge "$srcdir/bin/converge"
+    else
+        export STACK_ROOT="$srcdir/.stack-root"
+        msg "Building converge with stack (resolver: $(awk '/^resolver:/ {print $2}' stack.yaml))..."
+        stack build \
+            --copy-bins \
+            --local-bin-path "$srcdir/bin" \
+            --ghc-options '-O2'
+    fi
+}
+
+check() {
+    cd "$startdir"
+    export STACK_ROOT="$srcdir/.stack-root"
+    msg "Running tests..."
+    stack test
+}
+
+package() {
+    cd "$startdir"
+
+    # Binary
+    install -Dm755 "$srcdir/bin/converge" \
+        "$pkgdir/usr/bin/converge"
+
+    # User systemd service
+    install -Dm644 converge.service \
+        "$pkgdir/usr/lib/systemd/user/converge.service"
+
+    # Example config
+    install -Dm644 converge.example.yaml \
+        "$pkgdir/etc/converge/config.example.yaml"
+
+    # Documentation
+    install -Dm644 README.md \
+        "$pkgdir/usr/share/doc/converge/README.md"
+}