fix(ci): keep third_party mount, always build submodules in CI

The third_party volume mount is required for astrolabe/notes/oidc
development. Always checkout submodules and build the OIDC app in
all CI matrix jobs since the app container needs it.

Remove the docker-compose.oidc.yml override (no longer needed).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -35,7 +35,7 @@ services:
       - ./app-hooks:/docker-entrypoint-hooks.d:ro
       # Mount OIDC development directory outside /var/www/html to avoid rsync conflicts
       # The post-installation hook will register /opt/apps as an additional app directory
-      #- ./third_party:/opt/apps:ro
+      - ./third_party:/opt/apps:ro
     environment:
       - NEXTCLOUD_TRUSTED_DOMAINS=app
       - NEXTCLOUD_ADMIN_USER=admin