feat(portals): serve each portal with Caddy instead of nginx (refs #166)

nginx resolves a variable `proxy_pass` upstream itself, using only the `resolver`
directive and never the search domains in /etc/resolv.conf. That cost two
workarounds in one script: rewriting the resolver address for rootless podman
(Docker's 127.0.0.11 is wrong there), and injecting a full FQDN so the bare `bff`
name could resolve on Kubernetes at all.

Caddy dials its upstream per request through the system resolver, which reads
nameserver *and* search domains, so `reverse_proxy bff:8080` resolves on every
engine with no per-engine configuration — and it still starts before the BFF
exists and picks up its restarts. Both workarounds are deleted with the script.

Routing uses mutually-exclusive `handle` blocks, not a bare `try_files`: Caddy
sorts rewrites *before* reverse_proxy, so a top-level SPA fallback would rewrite
every API path to /index.html before the proxy saw it.

apps/openbaar/Caddyfile

@@ -0,0 +1,21 @@
+:80 {
+	# Same-origin API: the public register is anonymous, but still reads through the BFF (S-09).
+	# `handle` blocks are mutually exclusive and matched most-specific-first, so the
+	# SPA fallback below can never swallow an API call — unlike a bare `try_files`,
+	# which Caddy sorts *before* reverse_proxy and would rewrite it to /index.html.
+	#
+	# No `resolver` stanza is needed: Caddy dials the upstream per
+	# request through the system resolver, so it starts before the BFF is up, picks up
+	# its restarts, and honours the DNS search domains in /etc/resolv.conf — which is
+	# what lets the bare `bff` name resolve on Kubernetes as well as under compose.
+	handle /openbaar/* {
+		reverse_proxy bff:8080
+	}
+
+	# The Angular app. Client-side routing: an unknown path serves index.html.
+	handle {
+		root * /usr/share/caddy
+		try_files {path} /index.html
+		file_server
+	}
+}

apps/openbaar/Dockerfile

@@ -1,4 +1,4 @@
-# Multi-stage build for the openbaar portal (Angular → nginx).
+# Multi-stage build for the openbaar portal (Angular → Caddy).
 # Build context is the repo root (the app needs the pnpm workspace + libs). See infra/docker-compose.yml.
 FROM node:24-slim AS build
 WORKDIR /src
@@ -13,13 +13,9 @@ COPY apps/openbaar apps/openbaar
 COPY libs libs
 RUN pnpm nx build openbaar
 
-FROM nginx:1.27-alpine AS runtime
-COPY apps/openbaar/nginx.conf /etc/nginx/conf.d/default.conf
-COPY --from=build /src/dist/apps/openbaar/browser /usr/share/nginx/html
+FROM caddy:2-alpine AS runtime
+COPY apps/openbaar/Caddyfile /etc/caddy/Caddyfile
+COPY --from=build /src/dist/apps/openbaar/browser /usr/share/caddy
 # No runtime config: the openbaar register is anonymous (no OIDC authority to inject).
-# Make the reverse-proxy resolver engine-portable (Docker 127.0.0.11 vs podman aardvark); runs from
-# the nginx image's /docker-entrypoint.d before nginx starts.
-COPY apps/portal-nginx-resolver.sh /docker-entrypoint.d/40-resolver.sh
-RUN chmod +x /docker-entrypoint.d/40-resolver.sh
 
 EXPOSE 80

apps/openbaar/nginx.conf

@@ -1,23 +0,0 @@
-server {
-  listen 80;
-  server_name _;
-  root /usr/share/nginx/html;
-  index index.html;
-
-  # Resolve the BFF via Docker's embedded DNS at request time (variable proxy_pass), so nginx starts
-  # even before the BFF is up and picks up restarts — instead of failing to load the config.
-  resolver 127.0.0.11 ipv6=off valid=30s;
-
-  # Same-origin API: proxy the anonymous openbaar endpoint group to the bff service. The api-client
-  # uses relative URLs, so the browser calls this origin and nginx forwards to the BFF — no CORS.
-  location /openbaar/ {
-    set $bff http://bff:8080;
-    proxy_pass $bff;
-    proxy_set_header Host $host;
-  }
-
-  # SPA fallback — Angular client-side routing.
-  location / {
-    try_files $uri $uri/ /index.html;
-  }
-}

apps/openbaar/src/app/app.config.ts

@@ -8,7 +8,7 @@ import { appRoutes } from './app.routes';
 
 /**
  * The openbaar register is a public, anonymous read: no DigiD, no auth interceptor. The app is served
- * same-origin as the BFF (nginx proxies /openbaar), so the api-client's relative calls stay same-origin.
+ * same-origin as the BFF (Caddy proxies /openbaar), so the api-client's relative calls stay same-origin.
  */
 export const appConfig: ApplicationConfig = {
   providers: [