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/llm/orchestrator.py

@@ -0,0 +1,81 @@
+import json
+import logging
+import uuid
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+logger = logging.getLogger("app.llm.orchestrator")
+
+from app.config import settings
+from app.llm.client import get_dm_system_prompt, get_llm_client
+from app.llm.context import build_context
+from app.llm.tools import character_sheet, dice
+from app.models.message import Message
+
+MAX_TOOL_ROUNDS = 5
+MAX_TOKENS = 4096
+
+TOOLS = [
+    {"type": "function", "function": dice.TOOL_SCHEMA},
+    {"type": "function", "function": character_sheet.TOOL_SCHEMA},
+]
+
+
+async def _execute_tool_call(
+    session: AsyncSession, game_id: uuid.UUID, tool_name: str, tool_input: dict
+) -> dict:
+    """Runs one tool call. Errors are returned as a payload (not raised), so the DM sees them
+    as a tool result and can recover instead of the whole turn crashing."""
+    try:
+        if tool_name == "roll_dice":
+            return dice.roll(tool_input["notation"])
+        if tool_name == "upsert_character_sheet":
+            return await character_sheet.upsert(session, game_id, tool_input)
+        return {"error": f"Unknown tool {tool_name!r}"}
+    except Exception as exc:  # noqa: BLE001
+        logger.warning("Tool call %s failed: %s", tool_name, exc)
+        await session.rollback()
+        return {"error": str(exc)}
+
+
+async def run_dm_turn(session: AsyncSession, game_id: uuid.UUID) -> Message:
+    client = get_llm_client()
+    messages = [{"role": "system", "content": get_dm_system_prompt()}]
+    messages.extend(await build_context(session, game_id))
+
+    final_text = ""
+    for _ in range(MAX_TOOL_ROUNDS):
+        response = await client.chat.completions.create(
+            model=settings.dm_model,
+            max_tokens=MAX_TOKENS,
+            messages=messages,
+            tools=TOOLS,
+        )
+        choice = response.choices[0]
+        message = choice.message
+        final_text = message.content or ""
+
+        if not message.tool_calls:
+            break
+
+        messages.append(message.model_dump(exclude_unset=True))
+
+        for tool_call in message.tool_calls:
+            tool_input = json.loads(tool_call.function.arguments)
+            result = await _execute_tool_call(session, game_id, tool_call.function.name, tool_input)
+            messages.append(
+                {
+                    "role": "tool",
+                    "tool_call_id": tool_call.id,
+                    "content": json.dumps(result),
+                }
+            )
+    else:
+        if not final_text:
+            final_text = "(Der Dungeon Master braucht einen Moment länger als erwartet — bitte versuche es erneut.)"
+
+    dm_message = Message(game_id=game_id, sender_type="dm", content=final_text)
+    session.add(dm_message)
+    await session.commit()
+    await session.refresh(dm_message)
+    return dm_message