contract: card status 'waiting on a dependency'

tsk-tz6c39nhkac7 open

Oliver adopted this at the 2026-11-03 jour fixe (req-b2ckhrgzhfge).

Problem: a card that can't start until another card or PR is done (for example tsk-mcd2xwwa2fzv, which waits for #1294, or tsk-0aadqqwe8jvt after #1287) shows as open. maity resume and wake then push members to claim it, and a member either claims it and idles or has to explain why not.

Contract first (docs/api.md, one PR), then hub, CLI and web:

A way to mark a card as waiting on one or more named dependencies (card ids, optionally a PR). Decide in the contract whether that is a new status or a flag on open, with a short state table: who may set and clear it, and what happens when the dependency reaches done (back to open automatically, with an event).
resume, wake and the "claimable" lists don't offer a waiting card for claiming. The board and the card page show what it waits on.
Statistics count it neither as open work nor as stalled.
Check the reserved words and view lists in §16.11 in the same PR (see the note on contract changes breaking hub tests).