feat: rework OIDC to BFF (Backend-For-Frontend) cookie-session pattern

- backend: switch from OAuth2 Resource Server to OAuth2 Client (spring-boot-starter-oauth2-client)
- backend: configure Spring Security oauth2Login() with session cookie (JSESSIONID HttpOnly)
- backend: add UserController exposing /api/user to report authenticated user info
- backend: configure GET /logout with RP-initiated end-session support
- backend: update HelloController to use @AuthenticationPrincipal OAuth2User
- backend: update all tests to use .with(oidcLogin()) mock
- backend: explicitly configure OIDC provider endpoints to bypass discovery at test time
- frontend: remove angular-oauth2-oidc and @ngx-env/builder dependencies
- frontend: revert angular.json builders to standard @angular/build:*
- frontend: replace client-side OIDC flow with /api/user check + window.location redirects
- frontend: update app.config.ts and config.service.ts to remove OIDC configuration
- frontend: rewrite all unit tests to mock /api/user endpoint instead of OAuthService
- compose: move OIDC_CLIENT_ID and OIDC_CLIENT_SECRET to backend environment variables
- compose/dockerfile: remove frontend build-time OIDC ARG/ENV secrets

compose.yml

@@ -26,6 +26,8 @@ services:
     environment:
       SPRING_DATA_MONGODB_URI: mongodb://admin:adminpassword@mongodb:27017/lmnp?authSource=admin
       OIDC_ISSUER_URI: ${OIDC_ISSUER_URI:-http://localhost:8090/realms/voidAuth}
+      OIDC_CLIENT_ID: ${OIDC_CLIENT_ID:-lmnp-client}
+      OIDC_CLIENT_SECRET: ${OIDC_CLIENT_SECRET:-lmnp-secret}
     depends_on:
       mongodb:
         condition: service_healthy
@@ -34,10 +36,6 @@ services:
     build:
       context: ./frontend
       dockerfile: Dockerfile
-      args:
-        - OIDC_ISSUER_URI=${OIDC_ISSUER_URI:-http://localhost:8090/realms/voidAuth}
-        - OIDC_CLIENT_ID=${OIDC_CLIENT_ID:-lmnp-client}
-        - OIDC_CLIENT_SECRET=${OIDC_CLIENT_SECRET:-lmnp-secret}
     container_name: lmnp-frontend
     ports:
       - "80:80"