CUB-66: scaffold Angular frontend and add Dockerfile with nginx

- Scaffolded Angular 21 app in frontend/ (standalone, routing, scss)
- Multi-stage Dockerfile: node:22-alpine build → nginx:alpine serve
- nginx.conf with SPA routing fallback, API proxy, gzip, asset caching
- .dockerignore excludes node_modules, dist, .angular, spec files
- docker build → PASS, container serves UI on port 80 (HTTP 200)
- Final image: 92.9MB (nginx:alpine)

frontend/src/main.ts

@@ -0,0 +1,6 @@
+import { bootstrapApplication } from '@angular/platform-browser';
+import { appConfig } from './app/app.config';
+import { App } from './app/app';
+
+bootstrapApplication(App, appConfig)
+  .catch((err) => console.error(err));