Add version groups to share routes and boss battles across games

Routes and boss battles now belong to a version_group instead of
individual games, so paired versions (e.g. Red/Blue, Gold/Silver)
share the same route structure and boss battles. Route encounters
gain a game_id column to support game-specific encounter tables
within a shared route. Includes migration, updated seeds, API
changes, and frontend type updates.

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

backend/src/app/models/route.py

@@ -7,19 +7,21 @@ from app.core.database import Base
 class Route(Base):
     __tablename__ = "routes"
     __table_args__ = (
-        UniqueConstraint("game_id", "name", name="uq_routes_game_name"),
+        UniqueConstraint("version_group_id", "name", name="uq_routes_version_group_name"),
     )
 
     id: Mapped[int] = mapped_column(primary_key=True)
     name: Mapped[str] = mapped_column(String(100))
-    game_id: Mapped[int] = mapped_column(ForeignKey("games.id"), index=True)
+    version_group_id: Mapped[int] = mapped_column(
+        ForeignKey("version_groups.id"), index=True
+    )
     order: Mapped[int] = mapped_column(SmallInteger)
     parent_route_id: Mapped[int | None] = mapped_column(
         ForeignKey("routes.id", ondelete="CASCADE"), index=True, default=None
     )
     pinwheel_zone: Mapped[int | None] = mapped_column(SmallInteger, default=None)
 
-    game: Mapped["Game"] = relationship(back_populates="routes")
+    version_group: Mapped["VersionGroup"] = relationship(back_populates="routes")
     route_encounters: Mapped[list["RouteEncounter"]] = relationship(
         back_populates="route"
     )