Review follow-up on the share-link password UI:
- Removing a link's password makes it publicly watchable, a protection
downgrade; gate it behind a danger-confirm like the neighbouring Revoke,
spelling out that anyone with the URL can then watch without a password.
- When setting a first password the input reused the create-form "Password
(optional)" placeholder, but it's required here (Save stays disabled until
non-empty); use the "Set a password" wording instead.