Add pokemon evolution support across the full stack

- Evolution model with trigger, level, item, and condition fields
- Encounter.current_pokemon_id tracks evolved species separately
- Alembic migration for evolutions table and current_pokemon_id column
- Seed pipeline loads evolution data with manual overrides
- GET /pokemon/{id}/evolutions and PATCH /encounters/{id} endpoints
- Evolve button in StatusChangeModal with evolution method details
- PokemonCard shows evolved species with "Originally" label

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

backend/src/app/seeds/loader.py

@@ -4,6 +4,7 @@ from sqlalchemy import select
 from sqlalchemy.dialects.postgresql import insert
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.models.evolution import Evolution
 from app.models.game import Game
 from app.models.pokemon import Pokemon
 from app.models.route import Route
@@ -118,3 +119,36 @@ async def upsert_route_encounters(
         count += 1
 
     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
+    for evo in evolutions:
+        from_id = dex_to_id.get(evo["from_national_dex"])
+        to_id = dex_to_id.get(evo["to_national_dex"])
+        if from_id is None or to_id is None:
+            continue
+
+        evolution = Evolution(
+            from_pokemon_id=from_id,
+            to_pokemon_id=to_id,
+            trigger=evo["trigger"],
+            min_level=evo.get("min_level"),
+            item=evo.get("item"),
+            held_item=evo.get("held_item"),
+            condition=evo.get("condition"),
+        )
+        session.add(evolution)
+        count += 1
+
+    await session.flush()
+    return count