Game profile: granular IGDB platforms and free-game badge

- List IGDB platform names verbatim (Windows, MacOS) instead of
  coarse buckets; fall back to Steam OS flags and hardware
  distributors only when IGDB has none
- Show a Free badge instead of prices when best price is zero

lib/i18n/dictionaries/de.json

@@ -37,6 +37,7 @@
             "links": "Links",
             "reviews": "Bewertungen",
             "prices": "Preise",
+            "free": "Kostenlos",
             "bestPrice": "Bester Preis",
             "historyLow": "Historischer Tiefstpreis",
             "allPrices": "ITAD",