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/home/home.component.ts

@@ -1,25 +1,38 @@
-import { Component, OnInit } from '@angular/core';
-import { UserService } from 'src/app/services/user.service';
+import { ChangeDetectionStrategy, Component, inject, OnInit } from '@angular/core';
+import { MatSnackBar } from '@angular/material/snack-bar';
+
+import { httpErrorMessage } from 'src/app/helpers/http-error';
+import { Tutorial } from 'src/app/models/tutorial.model';
+import { TokenStorageService } from 'src/app/services/token-storage.service';
+import { TutorialService } from 'src/app/services/tutorial.service';
 
 @Component({
-    selector: 'app-home',
-    templateUrl: './home.component.html',
-    styleUrls: ['./home.component.scss'],
-    standalone: false
+  selector: 'app-home',
+  templateUrl: './home.component.html',
+  styleUrls: ['./home.component.scss'],
+  changeDetection: ChangeDetectionStrategy.Eager,
+  standalone: false
 })
 export class HomeComponent implements OnInit {
-  content?: string;
+  private readonly tutorialService = inject(TutorialService);
+  private readonly snackBar = inject(MatSnackBar);
 
-  constructor(private userService: UserService) { }
+  readonly isLoggedIn = inject(TokenStorageService).isLoggedIn();
+
+  tutorials: Tutorial[] = [];
+  loaded = false;
 
   ngOnInit(): void {
-    // this.userService.getPublicContent().subscribe(
-    //   (data : any) => {
-    //     this.content = data;
-    //   },
-    //   (err : any) => {
-    //     this.content = JSON.parse(err.error).message;
-    //   }
-    // );
+    this.tutorialService.getPublished().subscribe({
+      // На пустой результат сервер отвечает 204 без тела
+      next: data => {
+        this.tutorials = data ?? [];
+        this.loaded = true;
+      },
+      error: err => {
+        this.loaded = true;
+        this.snackBar.open(httpErrorMessage(err), 'OK', { duration: 5000 });
+      }
+    });
   }
-}
+}