Introduces full boss battle system: data models (BossBattle, BossPokemon,
BossResult), API endpoints for CRUD and per-run defeat tracking, and frontend
UI including a sticky level cap bar with badge display on the run page,
interleaved boss battle cards in the encounter list, and an admin panel
section for managing boss battles and their pokemon teams.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
