feat: finish demo — Angular 22 + Material UI, role management, schema and Docker cleanup

Frontend
- Upgrade Angular 19 -> 22 (TypeScript 6, new control flow), drop unused
  packages (bootstrap, jquery, popper, ng-bootstrap, webpack)
- Move the UI to Angular Material: toolbar with user menu, tutorials list,
  add/edit forms, admin users table with role editing dialog, profile,
  home page with published tutorials, registration form, login dialog
- Guard routes: login required for add/edit/profile, admin role for /admin
- Remove the /login, Moderator and User pages, event bus, auth interceptor
  and other dead code

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 (bigint ids, tutorials PK,
  identity ids); Hibernate now runs with ddl-auto: validate

Docker
- Three-stage Dockerfile (Node build, Gradle build, JRE runtime) with
  layer caching, non-root user and healthcheck; add .dockerignore
- docker-compose waits for a healthy Postgres, always rebuilds the image,
  no longer mounts the Docker socket

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

.dockerignore

@@ -0,0 +1,26 @@
+# Всё, что не нужно для сборки образа: ускоряет передачу контекста и не даёт
+# попасть внутрь Windows-бинарникам из node_modules и локальным секретам
+.git
+.gitignore
+.gitattributes
+.idea
+.vscode
+.gradle
+build
+*.iml
+
+.env
+.env.*
+!.env.example
+
+Dockerfile
+docker-compose*.yml
+.dockerignore
+
+spring-angular-ui/node_modules
+spring-angular-ui/.angular
+spring-angular-ui/static
+spring-angular-ui/dist
+
+# Собранный фронт собирается заново внутри образа
+src/main/resources/static