feat(portal-self-service): runtime config + nginx serve/proxy image (refs #68)

The app loads /config.json at startup (main.ts) so the OIDC authority is set per
environment from one build; appConfig becomes a factory and derives redirectUrl +
secureApiOrigin from the app origin (same-origin as the BFF). A multi-stage
Dockerfile builds the app and serves it via nginx, reverse-proxying /self-service
+ /openbaar to the bff (relative URLs → no CORS); nginx resolves the BFF at request
time. The compose image bakes config.json with the keycloak:8080 authority so the
browser's token issuer matches the BFF (ADR-0010).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/self-service/src/main.ts

@@ -1,5 +1,10 @@
 import { bootstrapApplication } from '@angular/platform-browser';
-import { appConfig } from './app/app.config';
 import { App } from './app/app';
+import { appConfig, type RuntimeConfig } from './app/app.config';
 
-bootstrapApplication(App, appConfig).catch((err) => console.error(err));
+// Load environment config before bootstrap so the OIDC authority is set per environment
+// (dev: localhost; compose: keycloak:8080) from a single build — 12-factor (S-08d).
+fetch('config.json')
+  .then((response) => response.json() as Promise<RuntimeConfig>)
+  .then((config) => bootstrapApplication(App, appConfig(config)))
+  .catch((err) => console.error(err));