feat(i18n): per-bundle LOCALE_ID + language switching under docker compose

Fix the hardcoded LOCALE_ID: 'nl' — provide it from $localize.locale (the build-time
locale, 'nl'/'en', undefined→'nl' in dev) and register both nl+en locale data, so the en
bundle formats dates/numbers correctly. Make `docker compose up` serve the LOCALIZED build:
the web service now runs `ng build --localize` then serve-i18n.mjs, which gained a PORT env
+ an /api reverse-proxy (API_PROXY_TARGET → the api container) so both /nl/ and /en/ are
served with the language switcher working end-to-end. Drop the now-unused proxy.conf.docker.json
(serve-i18n proxies /api itself); update ARCHITECTURE. `npm start` stays the nl-only HMR loop.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/reference/architecture/ARCHITECTURE.md

@@ -534,8 +534,9 @@ no longer hand-written DTOs — it's an **NSwag-generated typed client**
 - **Proxy.** The app uses a relative base URL (`apiBaseUrl: ''`), so `/api` calls are
   same-origin and `ng serve` proxies them to the backend on `:5000`.
   ([`environment.ts`](../../../src/environments/environment.ts),
-  [`proxy.conf.json`](../../../proxy.conf.json); `proxy.conf.docker.json` targets the
-  compose service.)
+  [`proxy.conf.json`](../../../proxy.conf.json)). Under `docker compose up` the app is served
+  localized (both locales) by `scripts/serve-i18n.mjs`, which proxies `/api` to the `api`
+  container itself (`API_PROXY_TARGET`).
 - **Client → HttpClient seam.** The NSwag client's `fetch` is routed through Angular's
   `HttpClient` by `httpClientFetch` — the one place cross-cutting concerns live:
   `X-Correlation-Id` on every call, `Idempotency-Key` on non-GETs, a 10 s timeout, and