Kura cache surface enabled by default on self-hosted servers

On a self-hosted Tuist server, the Kura cache surface, including the Cache page, sidebar entry, Usage page, and settings section, is now available by default. Previously, operators had to reach the /ops/flags UI and toggle the :kura feature flag before the Cache page would render, even though a self-hosted deployment already grants the self-hosted-cache entitlement. Self-hosters no longer need to flip the flag to generate the control-plane credential. The managed cache-server provisioning section of the Cache page (which is inert on self-hosted, since there are no managed regions or Tuist-managed Kubernetes) is also hidden in this mode, so self-hosters see only credential generation and the registered-nodes list. Hosted tuist.dev servers keep the existing :kura flag gating.