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/config.py

@@ -0,0 +1,26 @@
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", extra="ignore")
+
+    database_url: str = "postgresql+asyncpg://dnd:changeme@postgres:5432/dnd"
+
+    xai_api_key: str = ""
+    xai_base_url: str = "https://api.x.ai/v1"
+    dm_model: str = "grok-4.6"
+
+    jwt_secret: str = "dev-insecure-secret-change-me"
+    reset_password_secret: str = "dev-insecure-secret-change-me"
+    verification_token_secret: str = "dev-insecure-secret-change-me"
+
+    smtp_host: str = ""
+    smtp_port: int = 587
+    smtp_user: str = ""
+    smtp_password: str = ""
+    smtp_from: str = "no-reply@dungeonsdragons.tstratmann.de"
+
+    frontend_origin: str = "http://localhost:5173"
+
+
+settings = Settings()