Poll mirror status endpoint for clone readiness

Switch both repo mirror create <url> and the onboarding wizard onto one shared createAndAwaitMirror path that polls GetMirror for the new Mirror.status (processing/ready/failed/suspended) instead of the smart-HTTP info/refs probe. This drops the repo-scoped token dance and data-plane round trip; suspension and clone failure now surface directly from the control plane.

Removes the now-dead info/refs probe machinery (waitForMirrorClone, mirrorAdvertisesHead, checkProbeRedirect, the probe HTTP client and token source) and their tests.