workstream progress trusted the mutable STATE.md `Status` field, so a
shipped/archived milestone whose field was left at `executing` was reported
as executing — a stale hand-maintained field became the source of truth
instead of the authoritative archive/tag/ROADMAP signals.
Derive status in the inventory builder from a milestoneShipped signal
(archived milestone snapshot under milestones/, or a SHIPPED marker in the
workstream ROADMAP), collected by inspectWorkstream. The inventory now
reports `status_source` (field|derived) and `status_conflict` (true when
the derived value disagrees with the stale field), and a shipped workstream
is never reported executing.
- src/workstream-inventory-builder.cts: milestoneShipped input + status_source/status_conflict outputs + derivation
- src/workstream-inventory.cts: workstreamMilestoneShipped() signal detector wired into inspectWorkstream
- tests/workstream-inventory.test.cjs: regression (builder unit + inspectWorkstream integration + negative)
Closes#1913
