feat(macos): add code signing and notarization support

Add macOS code signing and notarization for Gatekeeper compatibility:

- Add hardened runtime configuration in package.json
- Add entitlements.mac.plist for required app permissions
- Enable built-in electron-builder notarization
- Add code signing and notarization secrets to workflow

Required GitHub Secrets:
- CSC_LINK: Base64-encoded .p12 certificate file
- CSC_KEY_PASSWORD: Password for the .p12 certificate
- APPLE_ID: Apple Developer account email
- APPLE_APP_SPECIFIC_PASSWORD: App-specific password from appleid.apple.com
- APPLE_TEAM_ID: 10-character Apple Developer Team ID

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -104,7 +104,12 @@
       ],
       "icon": "build/icon.icns",
       "artifactName": "${name}_${version}_${arch}.${ext}",
-      "category": "public.app-category.games"
+      "category": "public.app-category.games",
+      "hardenedRuntime": true,
+      "gatekeeperAssess": false,
+      "entitlements": "build/entitlements.mac.plist",
+      "entitlementsInherit": "build/entitlements.mac.plist",
+      "notarize": true
     },
     "nsis": {
       "oneClick": false,