fix(app-headless-cms): refresh revision list after create/delete

[brunozoric]

Summary

• Revision list refresh: After creating or deleting a revision, the revisions drawer now re-fetches the list from the API. Previously, the list stayed stale until the drawer was closed and reopened.
• Delete confirmation fix: The delete confirmation check used !confirmed which treated the dialog's undefined resolve as a cancellation. Changed to confirmed === false since onCancel explicitly resolves with false,
  while onConfirm() (called with no data) resolves with undefined.

Test plan

• Unit tests added for RevisionsListPresenter covering:
  • List refreshes after successful create
  • List refreshes after successful delete
  • No refresh on create/delete failure
  • No delete when confirmation is declined
  • Dispose clears all state
• Manual: open a content entry → open revisions drawer → create a new revision → verify the list updates immediately
• Manual: open revisions drawer → delete a draft revision → confirm → verify it's actually deleted and the list updates