RoMM: add app_info + optional_config metadata, add missing env vars

- Add app_info section: tagline, use cases, first steps, prerequisites, default creds
- Add optional_config: 6 metadata provider fields (IGDB, SteamGridDB, ScreenScraper, MobyGames)
- Add missing env vars to docker-compose.yml: SCREENSCRAPER_USER, SCREENSCRAPER_PASSWORD, MOBYGAMES_API_KEY
- Fix display_name: "ROMM" → "RomM"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/romm/docker-compose.yml

@@ -57,6 +57,9 @@ services:
       - IGDB_CLIENT_ID=${IGDB_CLIENT_ID:-}
       - IGDB_CLIENT_SECRET=${IGDB_CLIENT_SECRET:-}
       - STEAMGRIDDB_API_KEY=${STEAMGRIDDB_API_KEY:-}
+      - SCREENSCRAPER_USER=${SCREENSCRAPER_USER:-}
+      - SCREENSCRAPER_PASSWORD=${SCREENSCRAPER_PASSWORD:-}
+      - MOBYGAMES_API_KEY=${MOBYGAMES_API_KEY:-}
       - TZ=Europe/Budapest
     volumes:
       - ${HDD_PATH}/storage/romm/library:/romm/library