feat: add DMG build script and enhance README with installation instructions and Start at Login feature

apps/mac/AIWorkspace/scripts/build-dmg.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+APP_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+APP_NAME="AIWorkspace"
+DIST_DIR="$APP_ROOT/dist"
+APP_BUNDLE="$DIST_DIR/$APP_NAME.app"
+DMG_STAGING="$DIST_DIR/dmg-staging"
+DMG_PATH="$DIST_DIR/$APP_NAME.dmg"
+
+bash "$SCRIPT_DIR/package-app.sh"
+
+rm -rf "$DMG_STAGING" "$DMG_PATH"
+mkdir -p "$DMG_STAGING"
+cp -R "$APP_BUNDLE" "$DMG_STAGING/$APP_NAME.app"
+ln -s /Applications "$DMG_STAGING/Applications"
+
+hdiutil create \
+  -volname "AI Workspace" \
+  -srcfolder "$DMG_STAGING" \
+  -ov \
+  -format UDZO \
+  "$DMG_PATH"
+
+rm -rf "$DMG_STAGING"
+echo "Built $DMG_PATH"