feat: implement basic RPG mechanics with boss counter-attack

- Add Player and Boss data models (models.py)
- Implement command processing via regex matching (attack/heal/status)
- Add boss counter-attack mechanism (15 dmg per player attack)
- Add player death/respawn system (lose half gold, respawn full HP)
- Update frontend with boss HP bar, player stats panel, quick action buttons
- Add colored event log (red for attack, green for heal)
- Change port from 8000 to 8080

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

run.py

@@ -10,7 +10,7 @@ if __name__ == "__main__":
     uvicorn.run(
         "backend.app.main:app",
         host="0.0.0.0",
-        port=8000,
+        port=8080,
         reload=True,
         log_level="info"
     )