Add mac launcher, py2app setup, and build script

Co-authored-by: Copilot <[email protected]>

build_mac.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [ "$(uname)" != "Darwin" ]; then
+  echo "This build script must be run on macOS." >&2
+  exit 1
+fi
+
+python3 -m venv .venv
+source .venv/bin/activate
+
+pip install --upgrade pip setuptools wheel
+pip install -r requirements.txt
+pip install py2app
+
+# Build the macOS .app
+python3 setup.py py2app
+
+echo "Build complete. The application bundle is in dist/ (e.g. dist/mac_launcher.app)."