Handle 404 pages

[callmevladik]

Currently, when attempting to access a non-existing resource in the KRCI UI Portal, the user experiences an endless loading screen, which can be confusing. The goal of this task is to replace this behavior with a friendly error message that informs the user the requested resource does not exist. This approach should be applied universally across all resources within the portal.

Acceptance Criteria
A friendly error message is displayed whenever a user attempts to access a non-existing resource within the KRCI UI Portal.
The error message clearly communicates that the requested resource does not exist.
This error handling approach is consistently implemented across all resources in the portal.