feat: finish demo — port demo-monolith cleanup, separate UI and API containers

Frontend
- Bring spring-angular-ui back under version control with the Angular 22 +
  Material UI from demo-monolith; stop committing the built static/ folder
- Serve the UI from nginx, which proxies /api to the backend so the JWT
  cookie works on a single origin, and falls back to index.html for routes

Backend
- Add PUT /api/users/{id}/roles (admin only) that keeps at least one admin
  and does not let an admin drop their own admin role
- Tighten security: read tutorials publicly, change them only when logged
  in, users/roles API for admins only; hide password hashes in JSON
- Remove unused Settings and Test endpoints, DTO mappers, commented code
- Flyway V2 aligns the schema with the entities; Hibernate now runs with
  ddl-auto: validate
- JWT lifetime matches the 24h cookie; fix the cookie name typo
- Keep CORS only for calling the API directly (ng serve without proxy)

Docker
- Backend Dockerfile: Gradle build + JRE runtime with layer caching,
  non-root user and healthcheck; add .dockerignore
- UI Dockerfile: Node 24 build + nginx with healthcheck
- docker-compose runs its own Postgres, starts services in health order
  and always rebuilds images

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

spring-angular-ui/src/app/components/_tutorial-shared.scss

@@ -0,0 +1,75 @@
+// Общие стили экранов туториалов (список, добавление, редактирование)
+@use '@angular/material' as mat;
+
+.page {
+  max-width: 960px;
+  margin: 0 auto;
+}
+
+.page.narrow {
+  max-width: 560px;
+}
+
+.page-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 16px;
+  margin-bottom: 16px;
+}
+
+.page-title {
+  margin: 0;
+  font: var(--mat-sys-headline-small);
+  color: var(--mat-sys-on-surface);
+}
+
+a,
+a:hover {
+  text-decoration: none;
+}
+
+.status {
+  display: inline-block;
+  padding: 2px 10px;
+  border-radius: 8px;
+  font: var(--mat-sys-label-medium);
+  background-color: var(--mat-sys-surface-container-highest);
+  color: var(--mat-sys-on-surface-variant);
+}
+
+.status.published {
+  background-color: var(--mat-sys-tertiary-container);
+  color: var(--mat-sys-on-tertiary-container);
+}
+
+.empty {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 8px;
+  padding: 48px 16px;
+  text-align: center;
+  color: var(--mat-sys-on-surface-variant);
+
+  mat-icon {
+    width: 48px;
+    height: 48px;
+    font-size: 48px;
+    opacity: 0.6;
+  }
+
+  p {
+    margin: 0;
+  }
+}
+
+.danger {
+  @include mat.button-overrides((
+    text-label-text-color: var(--mat-sys-error),
+  ));
+}
+
+.full-width {
+  width: 100%;
+}