Add optimized multi-platform release CI/CD pipeline.

Split Windows builds into shared x64 prep and arch-specific packaging, add comprehensive caching, verification scripts, and a PR smoke workflow.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/ci-install-linux-packaging.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ARCH="${1:?usage: ci-install-linux-packaging.sh <x64|arm64>}"
+
+sudo apt-get update
+sudo apt-get install -y fakeroot rpm binutils libfuse2 wget file
+
+case "$ARCH" in
+  x64)
+    TOOL_URL="https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-x86_64.AppImage"
+    ;;
+  arm64)
+    TOOL_URL="https://github.com/AppImage/appimagetool/releases/download/continuous/appimagetool-aarch64.AppImage"
+    ;;
+  *)
+    echo "Unsupported arch: $ARCH" >&2
+    exit 1
+    ;;
+esac
+
+CACHE_DIR="${RUNNER_TOOL_CACHE:-/opt/hostedtoolcache}/appimagetool"
+mkdir -p "$CACHE_DIR"
+TOOL="$CACHE_DIR/appimagetool-${ARCH}.AppImage"
+if [[ ! -f "$TOOL" ]]; then
+  wget -q "$TOOL_URL" -O "$TOOL"
+  chmod +x "$TOOL"
+fi
+echo "APPIMAGETOOL=$TOOL" >> "$GITHUB_ENV"