Board status two-way: human board moves are signal, not noise #39

Why

The first board projection treats stage → Status as one-way outbound, and its
non-clobber guard is approximate: a human dragging a card to "Done" is moved
back to "In progress" on the next sync, because specsync only whitelists
status names it could have written, not what it actually last wrote. That
inverts the tool's philosophy — everywhere else (task checkboxes, issue
open/closed state) external changes are reconciled inbound, not overwritten.

A board move is a statement by a human. "Done" may mean the work is done
(the local change should complete/archive) — or the next sync may legitimately
push it back because tasks reopened. Reopening is real: an issue auto-closed by
a merge may be reopened because we were not actually done. The two sides need
merge semantics, not last-writer-wins.

What Changes

• Persist what specsync last wrote to the board (status option id, per
  change, in the gitignored .specsync/ state) so "specsync-managed" means
  "unchanged since specsync set it", exactly — not name-collision guessing.
• Reconcile board Status inbound before projecting outbound, mirroring
  checkbox reconcile:
  • human moved to a Done-like option, local tasks incomplete → surface it
    (report + optional stage override), do not silently drag the card back
  • human moved to an active option while local stage is complete → treat as
    reopen signal, consistent with -close-completed reopen semantics
  • no human move since last write → project stage → Status as today
• Define precedence with the issue open/closed lifecycle: auto-close on merge
  (-close-completed) closes the issue; the board Done follows the close, and
  a human reopen propagates back to both stage and Status.
• Cover all cases in faked-board tests: fresh card, specsync-set then
  untouched, human-moved forward, human-moved backward, reopened issue.

Out of scope

• Multi-board membership; custom fields beyond Status; assignee reconcile.

Capabilities

• board-status-reconcile: inbound board-status merge semantics.