Add game category and region metadata for genlocke presets

Add `category` field (original/remake/enhanced/sequel/spinoff) to the
Game model and tag all 38 games. Create regions.json with generation
mapping, ordering, and genlocke preset defaults per region. Add
GET /games/by-region endpoint returning games grouped by region.

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

backend/src/app/seeds/loader.py

@@ -51,6 +51,7 @@ async def upsert_games(
             "slug": game["slug"],
             "generation": game["generation"],
             "region": game["region"],
+            "category": game.get("category"),
             "release_year": game.get("release_year"),
             "color": game.get("color"),
         }
@@ -58,6 +59,7 @@ async def upsert_games(
             "name": game["name"],
             "generation": game["generation"],
             "region": game["region"],
+            "category": game.get("category"),
             "release_year": game.get("release_year"),
             "color": game.get("color"),
         }