refactor(docker): remove Keycloak and PostgreSQL services from production configuration

- Deleted PostgreSQL and Keycloak service definitions from docker-compose.prod.yml to streamline the deployment configuration.
- Updated README.md with new build arguments for API and Keycloak URLs.
- Adjusted Dockerfile.prod to ensure proper ownership for the application directory.

This change simplifies the production setup by removing unnecessary services.

frontend/Dockerfile.prod

@@ -59,6 +59,9 @@ COPY --from=build --chown=svelte:nodejs /app/build ./build
 COPY --from=build --chown=svelte:nodejs /app/package.json ./
 COPY --from=build --chown=svelte:nodejs /app/node_modules ./node_modules
 
+# WORKDIR /app queda owned por root; pnpm necesita crear _tmp_* en el cwd al ejecutar scripts.
+RUN chown svelte:nodejs /app
+
 USER svelte
 
 # Puerto para SvelteKit con adapter-node