feat: sprint 1 — auth + CRUD engagements

Ship the first feature end-to-end on the UI: users log in with JWT,
admins manage user accounts, and any authenticated user (per RBAC)
can create, list, view, edit, and delete engagements.

Backend (Flask + SQLAlchemy + SQLite, 63 pytest)
- User / Engagement models, Alembic 0001 initial schema
- argon2 password hashing, JWT bearer (60-min TTL), @login_required
  and @role_required decorators
- 13 API endpoints under /api/*, including last-admin protection on
  DELETE/PATCH user and JSON 404 on unknown /api/* paths
- `flask create-admin` CLI with duplicate / short-password handling

Frontend (React + Vite + Tailwind + TanStack Query, 20 vitest)
- Inter font bundled locally (no CDN), DESIGN.md tokens in Tailwind
- LoginPage / EngagementsList / EngagementForm / EngagementDetail /
  UsersAdmin pages with role-aware UI
- Layout, ProtectedRoute, StatusBadge, FormField, LoadingState,
  ErrorState, EmptyState, Toast + provider
- Axios client: Bearer interceptor, 401 → purge + /login + "Session
  expirée" toast, 403 → "Accès refusé" toast (declarative <Navigate>
  for already-authed users, Fragment-keyed admin user rows)

Deployment
- Single multistage Dockerfile (node:20-alpine → python:3.12-slim)
- docker/entrypoint.sh runs `flask db upgrade` before `flask run`
- Makefile: build/start/stop/restart/update/logs/create-admin/
  update-mitre/test-{backend,frontend,e2e}/clean
- .env.example documenting MIMIC_JWT_SECRET / MIMIC_DB_PATH / MIMIC_PORT
- SQLite at /data/mimic.sqlite on named volume mimic-data

Acceptance suite (Playwright, 36 tests, all 27 ACs)
- e2e/ scaffold with playwright.config + auth/api fixtures
- One spec per user story (us1-bootstrap through us6-deployment)
- Portable via MIMIC_CONTAINER_CMD / MIMIC_BASE_URL (docker or podman)

Docs
- README.md with quick-start and architecture overview
- CHANGELOG.md updated with Sprint 1 deliverables
- pyrightconfig.json so the Python LSP sees backend/.venv and
  resolves the `backend.app.*` absolute imports

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/serializers.py

@@ -0,0 +1,34 @@
+"""JSON serializers for API responses."""
+from __future__ import annotations
+
+from typing import Any
+
+from backend.app.models import Engagement, User
+
+
+def serialize_user(user: User) -> dict[str, Any]:
+    return {
+        "id": user.id,
+        "username": user.username,
+        "role": user.role.value,
+        "created_at": user.created_at.isoformat() if user.created_at else None,
+    }
+
+
+def serialize_user_brief(user: User) -> dict[str, Any]:
+    return {"id": user.id, "username": user.username}
+
+
+def serialize_engagement(engagement: Engagement) -> dict[str, Any]:
+    return {
+        "id": engagement.id,
+        "name": engagement.name,
+        "description": engagement.description,
+        "start_date": engagement.start_date.isoformat() if engagement.start_date else None,
+        "end_date": engagement.end_date.isoformat() if engagement.end_date else None,
+        "status": engagement.status.value,
+        "created_at": engagement.created_at.isoformat() if engagement.created_at else None,
+        "created_by": serialize_user_brief(engagement.created_by)  # type: ignore[arg-type]
+        if engagement.created_by
+        else None,
+    }