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/requirements.txt

@@ -0,0 +1,11 @@
+fastapi==0.115.6
+uvicorn[standard]==0.34.0
+sqlalchemy[asyncio]==2.0.36
+asyncpg==0.30.0
+alembic==1.14.0
+pydantic-settings==2.7.0
+fastapi-users[sqlalchemy]==14.0.1
+openai>=1.50.0,<2.0.0
+aiosmtplib==3.0.2
+python-multipart==0.0.20
+websockets==14.1