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/schemas/pokemon.py

@@ -11,6 +11,17 @@ class PokemonResponse(CamelModel):
     sprite_url: str | None
 
 
+class EvolutionResponse(CamelModel):
+    id: int
+    from_pokemon_id: int
+    to_pokemon: PokemonResponse
+    trigger: str
+    min_level: int | None
+    item: str | None
+    held_item: str | None
+    condition: str | None
+
+
 class RouteEncounterResponse(CamelModel):
     id: int
     route_id: int