Add boss seed data pipeline for export and import

Add seeder support for boss battles so new database instances come
pre-populated. Adds --export-bosses CLI flag to dump boss data from the
database to JSON seed files, and loads those files during normal seeding.

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

backend/src/app/seeds/loader.py

@@ -1,9 +1,11 @@
 """Database upsert helpers for seed data."""
 
-from sqlalchemy import select
+from sqlalchemy import delete, select
 from sqlalchemy.dialects.postgresql import insert
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.models.boss_battle import BossBattle
+from app.models.boss_pokemon import BossPokemon
 from app.models.evolution import Evolution
 from app.models.game import Game
 from app.models.pokemon import Pokemon
@@ -204,14 +206,69 @@ async def upsert_route_encounters(
     return count
 
 
+async def upsert_bosses(
+    session: AsyncSession,
+    version_group_id: int,
+    bosses: list[dict],
+    dex_to_id: dict[int, int],
+) -> int:
+    """Upsert boss battles for a version group, return count of bosses upserted."""
+    count = 0
+    for boss in bosses:
+        # Upsert the boss battle on (version_group_id, order) conflict
+        stmt = insert(BossBattle).values(
+            version_group_id=version_group_id,
+            name=boss["name"],
+            boss_type=boss["boss_type"],
+            badge_name=boss.get("badge_name"),
+            badge_image_url=boss.get("badge_image_url"),
+            level_cap=boss["level_cap"],
+            order=boss["order"],
+            location=boss["location"],
+            sprite_url=boss.get("sprite_url"),
+        ).on_conflict_do_update(
+            constraint="uq_boss_battles_version_group_order",
+            set_={
+                "name": boss["name"],
+                "boss_type": boss["boss_type"],
+                "badge_name": boss.get("badge_name"),
+                "badge_image_url": boss.get("badge_image_url"),
+                "level_cap": boss["level_cap"],
+                "location": boss["location"],
+                "sprite_url": boss.get("sprite_url"),
+            },
+        ).returning(BossBattle.id)
+        result = await session.execute(stmt)
+        boss_id = result.scalar_one()
+
+        # Delete existing boss_pokemon for this boss, then re-insert
+        await session.execute(
+            delete(BossPokemon).where(BossPokemon.boss_battle_id == boss_id)
+        )
+        for bp in boss.get("pokemon", []):
+            pokemon_id = dex_to_id.get(bp["pokeapi_id"])
+            if pokemon_id is None:
+                print(f"  Warning: no pokemon_id for pokeapi_id {bp['pokeapi_id']}")
+                continue
+            session.add(BossPokemon(
+                boss_battle_id=boss_id,
+                pokemon_id=pokemon_id,
+                level=bp["level"],
+                order=bp["order"],
+            ))
+
+        count += 1
+
+    await session.flush()
+    return count
+
+
 async def upsert_evolutions(
     session: AsyncSession,
     evolutions: list[dict],
     dex_to_id: dict[int, int],
 ) -> int:
     """Upsert evolution pairs, return count of upserted rows."""
-    # Clear existing evolutions and re-insert (simpler than complex upsert)
-    from sqlalchemy import delete
     await session.execute(delete(Evolution))
 
     count = 0