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-details/tutorial-details.component.ts

@@ -1,89 +1,78 @@
-import { Component, OnInit } from '@angular/core';
-import { TutorialService } from 'src/app/services/tutorial.service';
+import { ChangeDetectionStrategy, Component, inject, OnInit } from '@angular/core';
+import { HttpErrorResponse } from '@angular/common/http';
 import { ActivatedRoute, Router } from '@angular/router';
+import { MatSnackBar } from '@angular/material/snack-bar';
+
+import { httpErrorMessage } from 'src/app/helpers/http-error';
 import { Tutorial } from 'src/app/models/tutorial.model';
+import { TutorialService } from 'src/app/services/tutorial.service';
 
 @Component({
-    selector: 'app-tutorial-details',
-    templateUrl: './tutorial-details.component.html',
-    styleUrls: ['./tutorial-details.component.scss'],
-    standalone: false
+  selector: 'app-tutorial-details',
+  templateUrl: './tutorial-details.component.html',
+  styleUrls: ['./tutorial-details.component.scss'],
+  changeDetection: ChangeDetectionStrategy.Eager,
+  standalone: false
 })
 export class TutorialDetailsComponent implements OnInit {
+  private readonly tutorialService = inject(TutorialService);
+  private readonly route = inject(ActivatedRoute);
+  private readonly router = inject(Router);
+  private readonly snackBar = inject(MatSnackBar);
 
   currentTutorial: Tutorial = {
     title: '',
     description: '',
     published: false
   };
-  message = '';
-
-  constructor(
-    private tutorialService: TutorialService,
-    private route: ActivatedRoute,
-    private router: Router) { }
+  notFound = false;
 
   ngOnInit(): void {
-    this.message = '';
-    this.getTutorial(this.route.snapshot.params.id);
+    this.tutorialService.get(this.route.snapshot.params['id']).subscribe({
+      next: data => this.currentTutorial = data,
+      error: err => {
+        this.notFound = true;
+        this.showError(err);
+      }
+    });
   }
 
-  getTutorial(id: string): void {
-    this.tutorialService.get(id)
-      .subscribe(
-        data => {
-          this.currentTutorial = data;
-          console.log(data);
-        },
-        error => {
-          console.log(error);
-        });
-  }
-
-  updatePublished(status: boolean): void {
-    const data = {
-      title: this.currentTutorial.title,
-      description: this.currentTutorial.description,
-      published: status
-    };
-
-    this.message = '';
-
-    this.tutorialService.update(this.currentTutorial.id, data)
-      .subscribe(
-        response => {
-          this.currentTutorial.published = status;
-          console.log(response);
-          this.message = response.message ? response.message : 'The status was updated successfully!';
-        },
-        error => {
-          console.log(error);
-        });
+  updatePublished(published: boolean): void {
+    const data = { ...this.currentTutorial, published };
+    this.tutorialService.update(this.currentTutorial.id, data).subscribe({
+      next: () => {
+        this.currentTutorial.published = published;
+        this.notify(published ? 'Tutorial was published' : 'Tutorial was unpublished');
+      },
+      error: err => this.showError(err)
+    });
   }
 
   updateTutorial(): void {
-    this.message = '';
-
-    this.tutorialService.update(this.currentTutorial.id, this.currentTutorial)
-      .subscribe(
-        response => {
-          console.log(response);
-          this.message = response.message ? response.message : 'This tutorial was updated successfully!';
-        },
-        error => {
-          console.log(error);
-        });
+    this.tutorialService.update(this.currentTutorial.id, this.currentTutorial).subscribe({
+      next: () => this.notify('Tutorial was saved'),
+      error: err => this.showError(err)
+    });
   }
 
   deleteTutorial(): void {
-    this.tutorialService.delete(this.currentTutorial.id)
-      .subscribe(
-        response => {
-          console.log(response);
-          this.router.navigate(['/tutorials']);
-        },
-        error => {
-          console.log(error);
-        });
+    if (!confirm(`Delete "${this.currentTutorial.title}"?`)) {
+      return;
+    }
+    this.tutorialService.delete(this.currentTutorial.id).subscribe({
+      next: () => {
+        this.notify('Tutorial was deleted');
+        this.router.navigate(['/tutorials']);
+      },
+      error: err => this.showError(err)
+    });
   }
-}
+
+  private notify(message: string): void {
+    this.snackBar.open(message, 'OK', { duration: 3000 });
+  }
+
+  private showError(err: HttpErrorResponse): void {
+    this.snackBar.open(httpErrorMessage(err), 'OK', { duration: 5000 });
+  }
+}