feat(cloud): cloud agent last-run repo remember

[tatoalo]

Problem

Cloud task creation did not reliably remember the last selected repo and stale remembered repos could still leak into the cloud task flow

Changes

• persist last used cloud repo selection
• restore it safely after async settings hydration
• clear invalid remembered repos once gh repositories load (we could have scenarios in which user edit their repos and trigger tasks that couldn't end up in a good state from the get-go)