Reintroduce auth component changes

[schrodingersket]

Description

This PR brings back the authentication changes from https://github.com/sagemathinc/cocalc/pull/7238 (along with https://github.com/sagemathinc/cocalc/pull/7231 and https://github.com/sagemathinc/cocalc/pull/7251, which were also reverted in https://github.com/sagemathinc/cocalc/commit/2b88d398271ef856ad6e04a5f5e9642dba6cce89), modulo the changes to the landing page.

Testing Instructions:

• [ ] The most important thing to test here (other than logins) is using an anonymous account to run a notebook with an external license as described here: https://github.com/sagemathinc/cocalc/issues/7252.
• [ ] Verify that the Store sub-menu header in the CoCalc Store directs to the Store Overview page.
• [ ] Verify that the new link to the Voucher Center in the Store Overview page does in fact redirect to the Voucher Center.
• [ ] Verify that the license computation header shows correctly in mobile on the /store/site-license page.