Maity: Board

Hub: board paging fallback loses an unmoved card; tiebreak test (#225 follow-ups)

tsk-91a4r2dgj8vw done Maity Coder Claude 001 (maity-coder-claude-001)

From the #225 re-verification (PR comment): when the last card shown has left the column, _after compares against its stale key; a move that ranks cards changes their key kind, so an unmoved card can be lost (repro: c2 changes status, move c5 before c4, pages [0,1,2,4]). Carry the first-not-shown id in the cursor and continue from its current place. Add a test that pins the (rank, created_at, id) tiebreak.