docs: design doc for fup og fakta game engine + platform architecture

Captures all brainstormed decisions:
- Pluggable game cartridge platform (GameDriver interface)
- Celery + Redis timer-driven phase transitions
- Session owner play/pause/exit controls (no skip)
- Escalating scoring per round, incremental reveal scoring
- Emoji reactions during guess phase → post-game awards
- Relational per-user config presets with game-specific models
- Ephemeral game state (no persistence after exit/finish)
- Full WebSocket event reference and data lifecycle

Also: updated TODO.md (WebSocket done, persisted answers done),
created CLAUDE.md, and PROMPT.md for ralph-loop.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+**Weirsøe Party Protocol** is a Danish party game web platform (Jackbox-style) where games display on a primary screen and players participate via mobile. The MVP game is "Fup og Fakta" (a Fibbage-style lie-and-guess game).
+
+- Backend: Django 6.0.2 + Django Channels (WebSockets) + Redis
+- Frontend: Angular 19 shell + shared TypeScript API client library
+- Database: MySQL (SQLite fallback for dev)
+- Deployment: Proxmox LXC containers (not Docker)
+
+## Commands
+
+### Backend (Django)
+```bash
+python manage.py runserver       # Dev server
+python manage.py migrate         # Apply migrations
+python manage.py test            # Run all backend tests
+python manage.py test lobby      # Run tests for a single app
+python manage.py shell           # Django shell
+```
+
+### Frontend — API client (`/frontend`)
+```bash
+cd frontend
+npm install
+npm test       # Vitest unit tests
+npm run build  # TypeScript compile check (--noEmit)
+```
+
+### Frontend — Angular shell (`/frontend/angular`)
+```bash
+cd frontend/angular
+npm install
+npm start      # Dev server (ng serve)
+npm run build  # Production build
+npm run test   # Vitest unit tests
+```
+
+### i18n validation
+```bash
+python scripts/check_i18n_drift.py   # Check for key drift between locales
+```
+
+## Architecture
+
+### Backend apps
+
+| App | Purpose |
+|-----|---------|
+| `partyhub/` | Main Django project — settings, root URLs, ASGI/WSGI, i18n bootstrap |
+| `lobby/` | Session & player management — create/join session, locale-aware error responses |
+| `fupogfakta/` | Game logic — all domain models, score calculation (server-authoritative) |
+| `realtime/` | WebSocket event layer (stub) |
+| `voice/` | Voice/TTS interface (stub, Phase 2) |
+| `core_admin/` | Health endpoint (`/healthz`), global admin |
+
+**Key domain models** (all in `fupogfakta/models.py`): `GameSession`, `Player`, `Category`, `Question`, `RoundConfig`, `RoundQuestion`, `LieAnswer`, `Guess`, `ScoreEvent`.
+
+Score calculation is server-side only. `ScoreEvent` provides an auditable trail of all point changes.
+
+### Frontend layers
+
+1. **Shared API client** (`frontend/src/`) — pure TypeScript, framework-agnostic. Defines all API types (`api/types.ts`) and HTTP client abstraction (`api/client.ts`).
+2. **Angular shell** (`frontend/angular/`) — Angular 19 standalone components (no NgModules), hash-based routing. `host-shell.component` for the presenter screen; `player-shell.component` for mobile players.
+
+The Angular shell consumes the shared client via `frontend/src/api/angular-client.ts`.
+
+### Real-time flow
+
+`LOBBY → LIE → GUESS → REVEAL → FINISHED` — phase transitions broadcast a `PhaseViewModel` to all connected clients via WebSocket. Clients are read-only; only the server is authoritative for state.
+
+### i18n
+
+- **Single source of truth**: `shared/i18n/lobby.json` (keys in both `en` and `da`)
+- Loaded once at startup with LRU cache (`partyhub/i18n_bootstrap.py`)
+- Key naming: domain-first — `frontend.ui.host.*`, `frontend.ui.player.*`, `backend.errors.*`, `backend.error_codes.*`
+- Locale resolved from `Accept-Language` header; missing key returns key + logs warning; missing translation falls back to `en`
+
+## Key Conventions
+
+### Errors
+Backend error responses use stable machine-readable codes (`backend.error_codes.*`) with separately localized messages. Never couple error code strings to locale.
+
+### Game constraints (MVP)
+- 3–12 players per session
+- Session codes: 6-char alphanumeric (no 0/O/1/I/L)
+- Anti-cheat: no duplicate lies, lies cannot match the correct answer, answer order randomized
+
+### Git workflow
+- `main`: stable baseline
+- `feature/<name>`: development branches
+- `release/vX.Y.Z`: release preparation
+- Release: merge → create release branch → update `VERSION` + `CHANGELOG.md` → tag → push
+
+### TypeScript
+Strict mode required. Target ES2022. API response interfaces in `frontend/src/api/types.ts` must match backend responses exactly.
+
+### Database
+Use `ForeignKey` with explicit `on_delete` (`PROTECT`/`CASCADE`/`SET_NULL`). Add `db_index=True` on frequently queried fields. Migrations are auto-generated by Django and versioned in `migrations/`.
+
+## Environment Variables
+
+```
+DJANGO_SECRET_KEY, DJANGO_DEBUG, DJANGO_ALLOWED_HOSTS
+DB_ENGINE, DB_NAME, DB_USER, DB_PASSWORD, DB_HOST, DB_PORT
+CHANNEL_REDIS_HOST, CHANNEL_REDIS_PORT
+USE_SPA_UI (fallback: WPP_SPA_ENABLED)
+WPP_SPA_ASSET_BASE, WPP_SPA_ASSET_VERSION
+```
+
+## Test Files of Note
+
+- `lobby/tests.py` — comprehensive Django TestCase coverage for session/player/i18n/error flows
+- `frontend/angular/src/app/api-contract-smoke.spec.ts` — API contract smoke tests
+- `frontend/angular/src/app/lobby-i18n.spec.ts` — i18n parity checks
+- `frontend/tests/lobby-loader.parity.test.ts` — shared i18n loader parity