Add script to generate Play Store screenshot sizes

- Introduced a Node.js script (`playstore-screenshot-sizes.mjs`) to resize images for Play Store screenshots based on predefined profiles (phone, tablet-7, tablet-10).
- The script reads images from a specified input directory, processes them, and saves the resized images in an output directory with appropriate naming conventions.
- Added a Bash wrapper script (`playstore-screenshot-sizes.sh`) to execute the Node.js script easily from the command line.

package.json

@@ -23,6 +23,7 @@
     "publish-spielplan": "node scripts/publish-imported-spielplan.js",
     "playstore:assets": "./scripts/playstore-assets.sh",
     "playstore:anonymize": "./scripts/anonymize-playstore-screenshot.sh",
+    "playstore:screenshots": "./scripts/playstore-screenshot-sizes.sh",
     "test:watch": "vitest watch",
     "lint": "eslint . --fix"
   },