Fix GitHub Actions workflow: update artifact path and Keycloak service configuration

- Fix Next.js build artifact path from web/.next to web/build (matches distDir config)
- Fix Keycloak service: remove invalid 'command' field, use --entrypoint in options
- Add KC_DB=dev-file for in-memory H2 database
- Configure Keycloak to start in dev mode via entrypoint

Author: felixevers

.github/workflows/tests.yml

@@ -91,7 +91,9 @@ jobs:
           --health-timeout 10s
           --health-retries 30
           --health-start-period 40s
-          --entrypoint /opt/keycloak/bin/kc.sh start-dev
+          --entrypoint /bin/sh
+          -c
+          "/opt/keycloak/bin/kc.sh start-dev"
         ports:
           - 8080:8080