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/schemas/message.py

@@ -0,0 +1,19 @@
+import uuid
+from datetime import datetime
+
+from pydantic import BaseModel
+
+
+class MessageRead(BaseModel):
+    id: int
+    sender_type: str
+    user_id: uuid.UUID | None
+    player_name: str | None
+    character_id: uuid.UUID | None
+    character_name: str | None
+    content: str
+    created_at: datetime
+
+
+class MessageCreate(BaseModel):
+    content: str