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-macos-dmg.sh

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if ! command -v create-dmg >/dev/null 2>&1; then
+  brew install create-dmg
+fi
+
+DMG_DIR="app/desktop/dmg-background"
+if [[ ! -f "$DMG_DIR/node_modules/playwright/package.json" ]]; then
+  npm --prefix "$DMG_DIR" install --no-fund --no-audit
+  npm --prefix "$DMG_DIR" exec playwright install chromium
+fi