Add Flatpak packaging for Patchwork 5.4.0

Bundle Poncho Wonky (Patchwork 5.4.0) for x86_64 and aarch64 on the
24.08 freedesktop runtime with the Electron BaseApp. Launcher forces
Wayland when a socket is present so the app starts from terminals
outside the desktop session. Pinned versions and checksums live in
versions.sh and are validated by check-versions.sh.

build.sh

@@ -0,0 +1,37 @@
+#!/bin/bash
+set -euo pipefail
+
+source "$(dirname "$0")/versions.sh"
+
+RUNTIME="org.freedesktop.Platform"
+SDK="org.freedesktop.Sdk"
+BASEAPP="org.electronjs.Electron2.BaseApp"
+APP_ID="nz.scuttlebutt.Patchwork"
+MANIFEST="nz.scuttlebutt.Patchwork.yaml"
+REPO="repo"
+BUILD_DIR="build-dir"
+
+# 1. Install build dependencies (runtime, SDK and Electron base app)
+flatpak install -y flathub \
+  "${RUNTIME}//${RUNTIME_VERSION}" \
+  "${SDK}//${RUNTIME_VERSION}" \
+  "${BASEAPP}//${RUNTIME_VERSION}"
+
+# 2. Build the bundle
+if ! command -v flatpak-builder >/dev/null 2>&1; then
+  echo "flatpak-builder is not installed." >&2
+  echo "Install it with one of:" >&2
+  echo "  sudo apt install flatpak-builder" >&2
+  echo "  flatpak install flathub org.flatpak.Builder" >&2
+  echo "If you used org.flatpak.Builder, run:" >&2
+  echo "  flatpak run --command=flatpak-builder org.flatpak.Builder --repo=${REPO} --force-clean ${BUILD_DIR} ${MANIFEST}" >&2
+  exit 1
+fi
+flatpak-builder --repo="${REPO}" --force-clean "${BUILD_DIR}" "${MANIFEST}"
+
+# 3. Install it into the current user
+flatpak --user remote-add --if-not-exists --no-gpg-verify patchwork-repo "${REPO}"
+flatpak --user install -y patchwork-repo "${APP_ID}"
+
+echo
+echo "Done. Run it with: flatpak run ${APP_ID}"