fix: ensure SSR always fetches fresh assets from database

Root cause: Dockerfile copied only browser/ to nginx; server/server.mjs
was built but never deployed or executed. Prerender baked DEFAULT_CONFIG
into static HTML with no API at build time, causing stale content on
every initial paint.

Changes:
- Dockerfile: serve stage uses node:22-alpine, installs nginx via apk,
  copies both browser/ and server/ bundles from build stage
- docker-entrypoint.sh: starts Angular SSR Node process on port 4200,
  waits for readiness, exports SSR_API_BASE_URL, then exec nginx
- nginx.conf.template: adds upstream ssr_backend block (127.0.0.1:4200),
  proxies / to SSR backend, static assets served directly with 1y cache
- app.server.routes.ts: all routes switched from RenderMode.Prerender
  to RenderMode.Server for zero stale content
- server.ts: removed dead prerender code (PRERENDERED_ROUTES,
  isPrerenderedRoute, allowStaticRouteRender)
- main.server.ts: injects SSR-aware apiBaseUrl via APP_CONFIG
  (reads SSR_API_BASE_URL env var)
- server.spec.ts: updated 5 test suites + added 5 new suites (31 tests)
  covering server.ts cleanup, RenderMode.Server, entrypoint lifecycle,
  Dockerfile build, nginx upstream proxy, and API URL injection
- vitest.config.ts: added server.spec.ts to include pattern

Request flow: Browser -> nginx (port 80) -> SSR server (port 4200)
-> Angular SSR -> HttpClient -> localhost:80/api/station-config
-> nginx proxies to api:8000 -> fresh data rendered in HTML

Dockerfile

@@ -7,8 +7,10 @@ COPY . .
 RUN npx ng build --configuration production
 
 # ── Serve stage ────────────────────────────────────────────────────────
-FROM docker.io/library/nginx:alpine
+FROM docker.io/library/node:22-alpine
+RUN apk add --no-cache nginx
 COPY --from=build /app/dist/radio-station/browser /usr/share/nginx/html
+COPY --from=build /app/dist/radio-station/server /app/server
 COPY nginx.conf.template /etc/nginx/conf.d/nginx.conf.template
 COPY config.json.template /usr/share/nginx/html/config.json.template
 COPY docker-entrypoint.sh /docker-entrypoint.sh