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>

scripts/serve-i18n.mjs

@@ -4,12 +4,15 @@
 // Plain `ng serve` (npm start) serves only nl at /, so switching 404s there — this static
 // server serves both locale subdirs with per-locale SPA fallback (a miss under /<locale>/…
 // serves that locale's index.html), so deep-link switches resolve. Demo only, not prod infra.
-import { createServer } from 'node:http';
+import { createServer, request as httpRequest } from 'node:http';
 import { readFile } from 'node:fs/promises';
 import { join, extname, normalize } from 'node:path';
 
 const ROOT = 'dist/atomic-design-poc/browser';
-const PORT = 4300;
+const PORT = Number(process.env.PORT ?? 4300);
+// Reverse-proxy /api → backend so the served app is the whole demo, not just static pages.
+// Docker sets API_PROXY_TARGET=http://api:5000; locally it defaults to the dev backend.
+const API_TARGET = new URL(process.env.API_PROXY_TARGET ?? 'http://localhost:5000');
 const MIME = {
   '.html': 'text/html',
   '.js': 'text/javascript',
@@ -28,7 +31,27 @@ const send = (res, status, body, type) => {
 };
 
 createServer(async (req, res) => {
-  const url = decodeURIComponent((req.url ?? '/').split('?')[0]);
+  const rawUrl = req.url ?? '/';
+  // Proxy API calls to the backend (keep the raw url incl. query).
+  if (rawUrl.startsWith('/api')) {
+    const proxied = httpRequest(
+      {
+        hostname: API_TARGET.hostname,
+        port: API_TARGET.port,
+        path: rawUrl,
+        method: req.method,
+        headers: req.headers,
+      },
+      (pr) => {
+        res.writeHead(pr.statusCode ?? 502, pr.headers);
+        pr.pipe(res);
+      },
+    );
+    proxied.on('error', () => send(res, 502, 'Bad gateway (API)', 'text/plain'));
+    req.pipe(proxied);
+    return;
+  }
+  const url = decodeURIComponent(rawUrl.split('?')[0]);
   // Landing at / has no locale bundle — redirect to Dutch.
   if (url === '/') {
     res.writeHead(302, { location: '/nl/' });