API: cursor pagination for list commands #40

List commands return everything: issue list takes only --state, repo log pages by sha but nothing else does. A CLI user with 40 issues never notices; a client rendering a list over a mobile connection does, and so does an instance with real volume.

Not blocking a first client — deliberately deferred until screens exist, because the right page sizes and cursor shapes are learned from real call patterns rather than guessed. Filing so the gap is recorded.

Wants an opaque cursor rather than offsets, consistent across issue list, mr list, repo list and the activity feed.