Self-follow check used get_attribute(:follower_id) which is nil at
validation time because relate_actor runs after validations in Ash.
Fixed to use context.actor.id directly.
Added 9 tests covering: follow, follow idempotency, self-follow
prevention, guest restriction, unfollow, unfollow noop,
guest unfollow, follower/following counts, and am_i_following.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
