build: add AppImage packaging pipeline and build scripts

packaging/appimage/build-appimage.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+APPIMAGE_ROOT="${ROOT_DIR}/appimage"
+BUILD_DIR="${APPIMAGE_ROOT}/build"
+APPDIR="${BUILD_DIR}/AppDir"
+DIST_DIR="${APPIMAGE_ROOT}/dist"
+
+APPIMAGE_BUILDER_BIN="${APPIMAGE_BUILDER_BIN:-appimage-builder}"
+
+for cmd in uv "${APPIMAGE_BUILDER_BIN}"; do
+    if ! command -v "${cmd}" >/dev/null 2>&1; then
+        echo "Missing required command: ${cmd}" >&2
+        echo "See docs/appimage.md for setup instructions." >&2
+        exit 1
+    fi
+done
+
+mkdir -p "${BUILD_DIR}" "${DIST_DIR}"
+rm -rf "${APPDIR}"
+mkdir -p "${APPDIR}"
+
+cd "${ROOT_DIR}"
+uv export \
+  --frozen \
+  --no-dev \
+  --no-emit-project \
+  --no-hashes \
+  --format requirements-txt \
+  --output-file "${BUILD_DIR}/requirements.txt"
+uv build --wheel --out-dir "${BUILD_DIR}"
+
+WHEEL_PATH="$(ls -1 "${BUILD_DIR}"/scanslicer-*.whl | head -n 1)"
+if [[ -z "${WHEEL_PATH}" ]]; then
+    echo "Could not find built wheel in ${BUILD_DIR}" >&2
+    exit 1
+fi
+printf "%s\n" "${WHEEL_PATH}" >> "${BUILD_DIR}/requirements.txt"
+
+export SCANSLICER_ROOT="${ROOT_DIR}"
+export SCANSLICER_APPDIR="${APPDIR}"
+export SCANSLICER_REQUIREMENTS="${BUILD_DIR}/requirements.txt"
+
+cd "${BUILD_DIR}"
+"${APPIMAGE_BUILDER_BIN}" --recipe "${ROOT_DIR}/packaging/appimage/AppImageBuilder.yml"
+
+mkdir -p "${DIST_DIR}"
+find "${BUILD_DIR}" -maxdepth 1 -type f \( -name "*.AppImage" -o -name "*.zsync" \) -exec mv -f {} "${DIST_DIR}/" \;
+
+echo "AppImage build complete. Output in ${DIST_DIR}"