Add Phase 1 MVP: D&D text-adventure server

FastAPI + Postgres backend with fastapi-users auth, games/characters
CRUD, and a WebSocket chat endpoint where an x.ai Grok DM narrates
play, rolls dice, and maintains character sheets via tool calls.
React + Tailwind frontend covers registration/login, game list and
creation, participation-code join flow, character viewer, and a
real-time chat session view. Docker Compose skeleton (Postgres +
backend) included; Caddy/frontend container wiring is deferred to
the deploy milestone.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -0,0 +1,6 @@
+from app.models.character import Character
+from app.models.game import Game, GameParticipant
+from app.models.message import Message
+from app.models.user import User
+
+__all__ = ["User", "Game", "GameParticipant", "Character", "Message"]