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_encounter.py

@@ -8,13 +8,15 @@ class RouteEncounter(Base):
     __tablename__ = "route_encounters"
     __table_args__ = (
         UniqueConstraint(
-            "route_id", "pokemon_id", "encounter_method", name="uq_route_pokemon_method"
+            "route_id", "pokemon_id", "encounter_method", "game_id",
+            name="uq_route_pokemon_method_game"
         ),
     )
 
     id: Mapped[int] = mapped_column(primary_key=True)
     route_id: Mapped[int] = mapped_column(ForeignKey("routes.id"), index=True)
     pokemon_id: Mapped[int] = mapped_column(ForeignKey("pokemon.id"), index=True)
+    game_id: Mapped[int] = mapped_column(ForeignKey("games.id"), index=True)
     encounter_method: Mapped[str] = mapped_column(String(30))
     encounter_rate: Mapped[int] = mapped_column(SmallInteger)
     min_level: Mapped[int] = mapped_column(SmallInteger)
@@ -22,6 +24,7 @@ class RouteEncounter(Base):
 
     route: Mapped["Route"] = relationship(back_populates="route_encounters")
     pokemon: Mapped["Pokemon"] = relationship(back_populates="route_encounters")
+    game: Mapped["Game"] = relationship()
 
     def __repr__(self) -> str:
         return f"<RouteEncounter(route_id={self.route_id}, pokemon_id={self.pokemon_id}, method='{self.encounter_method}')>"