create-a-container: use authentication checking middleware

[runleveldev]

Issue: Centralize authentication logic using middleware and add login redirect support

Description:
Endpoints currently perform authentication checks manually, e.g.:

if (!req.session.user) {

This duplicates logic across routes and makes maintenance error-prone.

Recommendation:

• Implement a shared authentication middleware that validates the session and either continues or redirects to the login page.
• Add a redirect query parameter to the login page so users are returned to their original destination after successful authentication.

Benefits:

• Reduces code duplication and improves consistency
• Simplifies adding new protected routes
• Provides smoother user experience with post-login redirects