Add game data seeding from PokeAPI with level ranges

Seed the database with Pokemon game data for 5 games (FireRed, LeafGreen,
Emerald, HeartGold, SoulSilver) using pokebase. Includes Alembic migrations
for route unique constraints and encounter level ranges, a two-phase seed
system (offline fetch to JSON, then idempotent upserts), and Dockerfile
updates for the seed runner.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/app/models/route.py

@@ -1,4 +1,4 @@
-from sqlalchemy import ForeignKey, SmallInteger, String
+from sqlalchemy import ForeignKey, SmallInteger, String, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.core.database import Base
@@ -6,6 +6,9 @@ from app.core.database import Base
 
 class Route(Base):
     __tablename__ = "routes"
+    __table_args__ = (
+        UniqueConstraint("game_id", "name", name="uq_routes_game_name"),
+    )
 
     id: Mapped[int] = mapped_column(primary_key=True)
     name: Mapped[str] = mapped_column(String(100))