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/alembic/versions/a1b2c3d4e5f8_add_category_to_games.py

@@ -0,0 +1,29 @@
+"""add category to games
+
+Revision ID: a1b2c3d4e5f8
+Revises: f6a7b8c9d0e1
+Create Date: 2026-02-09 12:00:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = 'a1b2c3d4e5f8'
+down_revision: Union[str, Sequence[str], None] = 'f6a7b8c9d0e1'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        'games',
+        sa.Column('category', sa.String(20), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column('games', 'category')