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/ws_tickets.py

@@ -0,0 +1,24 @@
+import secrets
+import time
+import uuid
+
+TICKET_TTL_SECONDS = 30
+
+_tickets: dict[str, tuple[uuid.UUID, uuid.UUID, float]] = {}  # ticket -> (game_id, user_id, expires_at)
+
+
+def issue_ticket(game_id: uuid.UUID, user_id: uuid.UUID) -> str:
+    ticket = secrets.token_urlsafe(32)
+    _tickets[ticket] = (game_id, user_id, time.monotonic() + TICKET_TTL_SECONDS)
+    return ticket
+
+
+def consume_ticket(ticket: str, game_id: uuid.UUID) -> uuid.UUID | None:
+    """Single-use: returns the user_id if the ticket is valid for this game and not expired, else None."""
+    entry = _tickets.pop(ticket, None)
+    if entry is None:
+        return None
+    ticket_game_id, user_id, expires_at = entry
+    if ticket_game_id != game_id or time.monotonic() > expires_at:
+        return None
+    return user_id