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/components/Toast.tsx

@@ -0,0 +1,47 @@
+import { useToast } from '@/hooks/useToast';
+
+/**
+ * Stack of toast notifications anchored bottom-right.
+ * Pure DESIGN.md surfaces: rounded-xl, soft-lift, ink slab for errors.
+ */
+export function ToastViewport(): JSX.Element {
+  const { toasts, dismiss } = useToast();
+  return (
+    <div
+      aria-live="polite"
+      aria-atomic="true"
+      className="fixed bottom-xl right-xl z-50 flex flex-col gap-sm w-[320px] pointer-events-none"
+    >
+      {toasts.map((t) => {
+        const isError = t.kind === 'error';
+        const isSuccess = t.kind === 'success';
+        const surface = isError
+          ? 'bg-ink text-ink-on'
+          : isSuccess
+            ? 'bg-primary text-ink-on'
+            : 'bg-canvas text-ink border border-hairline';
+        return (
+          <div
+            key={t.id}
+            role="status"
+            data-testid="toast"
+            data-kind={t.kind}
+            className={`pointer-events-auto rounded-xl px-md py-sm shadow-soft-lift text-[14px] leading-[1.4] ${surface}`}
+          >
+            <div className="flex items-start justify-between gap-sm">
+              <span className="flex-1">{t.message}</span>
+              <button
+                type="button"
+                onClick={() => dismiss(t.id)}
+                aria-label="Dismiss notification"
+                className="text-current opacity-70 hover:opacity-100"
+              >
+                ×
+              </button>
+            </div>
+          </div>
+        );
+      })}
+    </div>
+  );
+}