Enhance boss battles with more detailed information for each boss pokemon and the player's team.
## Boss Pokemon Details
Add the following optional fields to boss pokemon entries:
- **Ability** – the pokemon's ability
- **Held item** – item the pokemon is holding
- **Nature** – the pokemon's nature
- **Moveset** – up to 4 moves per pokemon
This requires backend model/schema changes (BossPokemon fields), migration, admin UI for editing, and display in the run encounter boss cards.
## Team Snapshot
When recording a boss battle result, allow the player to snapshot which of their alive team pokemon they used and at what levels. This gives a record of "what I brought to the fight."
- Add a `boss_result_team` join table (boss_result_id, encounter_id, level)
- In the BossDefeatModal, show checkboxes for alive team members with optional level override
- Display the team snapshot when viewing past boss results
