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>

frontend/src/hooks/useToast.tsx

@@ -0,0 +1,58 @@
+import {
+  createContext,
+  useCallback,
+  useContext,
+  useMemo,
+  useRef,
+  useState,
+  type ReactNode,
+} from 'react';
+
+export type ToastKind = 'info' | 'success' | 'error';
+
+export interface Toast {
+  id: number;
+  message: string;
+  kind: ToastKind;
+}
+
+interface ToastContextValue {
+  toasts: Toast[];
+  push: (message: string, kind?: ToastKind) => void;
+  dismiss: (id: number) => void;
+}
+
+const ToastContext = createContext<ToastContextValue | null>(null);
+
+const DEFAULT_DURATION_MS = 4000;
+
+export function ToastProvider({ children }: { children: ReactNode }): JSX.Element {
+  const [toasts, setToasts] = useState<Toast[]>([]);
+  const counterRef = useRef(0);
+
+  const dismiss = useCallback((id: number) => {
+    setToasts((prev) => prev.filter((t) => t.id !== id));
+  }, []);
+
+  const push = useCallback(
+    (message: string, kind: ToastKind = 'info') => {
+      counterRef.current += 1;
+      const id = counterRef.current;
+      setToasts((prev) => [...prev, { id, message, kind }]);
+      setTimeout(() => dismiss(id), DEFAULT_DURATION_MS);
+    },
+    [dismiss],
+  );
+
+  const value = useMemo(() => ({ toasts, push, dismiss }), [toasts, push, dismiss]);
+
+  return <ToastContext.Provider value={value}>{children}</ToastContext.Provider>;
+}
+
+export function useToast(): ToastContextValue {
+  const ctx = useContext(ToastContext);
+  if (!ctx) {
+    throw new Error('useToast must be used inside ToastProvider');
+  }
+  return ctx;
+}