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/profile/profile.component.html

@@ -1,26 +1,28 @@
-<div class="container" *ngIf="currentUser; else loggedOut">
-    <header class="jumbotron">
-      <h3>
-        <strong>{{ currentUser.username }}</strong> Profile
-      </h3>
-    </header>
-    <p>
-      <strong>Token:</strong>
-      {{ currentUser.accessToken.substring(0, 20) }} ...
-      {{ currentUser.accessToken.substr(currentUser.accessToken.length - 20) }}
-    </p>
-    <p>
-      <strong>Email:</strong>
-      {{ currentUser.email }}
-    </p>
-    <strong>Roles:</strong>
-    <ul>
-      <li *ngFor="let role of currentUser.roles">
-        {{ role }}
-      </li>
-    </ul>
-  </div>
-  
-  <ng-template #loggedOut>
-    Please login.
-  </ng-template>
+<div class="page narrow">
+  <mat-card appearance="outlined" class="profile-card">
+    <div class="hero">
+      <span class="avatar large">{{ user.username?.slice(0, 2) }}</span>
+      <h1 class="name">{{ user.username }}</h1>
+      <div class="roles">
+        @for (role of roles; track role) {
+          <span class="role {{ role }}">{{ roleLabel(role) }}</span>
+        }
+      </div>
+    </div>
+
+    <mat-divider></mat-divider>
+
+    <mat-list>
+      <mat-list-item>
+        <mat-icon matListItemIcon>person</mat-icon>
+        <span matListItemTitle>Username</span>
+        <span matListItemLine>{{ user.username }}</span>
+      </mat-list-item>
+      <mat-list-item>
+        <mat-icon matListItemIcon>mail</mat-icon>
+        <span matListItemTitle>Email</span>
+        <span matListItemLine>{{ user.email }}</span>
+      </mat-list-item>
+    </mat-list>
+  </mat-card>
+</div>