feat(infra): Keycloak with four mock realms (closes #3) (#43)

infra/keycloak/docker-compose.yml

@@ -0,0 +1,29 @@
+# Keycloak (S-02) with four pre-seeded realms imported at boot:
+#   digid · eherkenning · eidas · medewerker
+# Dev mode, H2 in-memory store, realm JSONs imported from ./realms.
+#
+#   docker compose -f infra/keycloak/docker-compose.yml up -d
+#   curl -s -o /dev/null -w '%{http_code}\n' \
+#     http://localhost:8180/realms/digid/.well-known/openid-configuration   # -> 200
+#
+# Admin console: http://localhost:8180/  (admin / admin — dev only)
+services:
+  keycloak:
+    image: quay.io/keycloak/keycloak:26.1
+    command: ["start-dev", "--import-realm"]
+    environment:
+      KC_BOOTSTRAP_ADMIN_USERNAME: admin
+      KC_BOOTSTRAP_ADMIN_PASSWORD: admin
+      # Older var names too, harmless on 26.x:
+      KEYCLOAK_ADMIN: admin
+      KEYCLOAK_ADMIN_PASSWORD: admin
+      KC_HEALTH_ENABLED: "true"
+      KC_HTTP_ENABLED: "true"
+    ports:
+      - "8180:8080"
+    volumes:
+      - ./realms:/opt/keycloak/data/import:ro,z
+    networks: [cg]
+
+networks:
+  cg: