D1146 — Retirements are rows of the Activity timeline, not a tab of their own

Decision. This amends D820, whose route and archive rules stand: the Retired tab of Activity is gone, and a concept that is archived, deprecated or superseded shows on the Activity timeline as the row of its change, with a pill naming its status in place of the change pill and, under the title, what replaced it, why and where it was. The summary counts the retired rows of the window. GET /api/ui/v1/kbs/{kb}/retired stays and is what the timeline reads; ?panel=retired opens Activity. A window with no change shows a quiet notice in place of the summary and, under it, the newest earlier changes on the same timeline, read in the same round as the window so the page never shows the notice alone while they load (a failed read leaves the notice without them).

Why. Activity is a timeline bounded by the window the reader picks; Retired was an inventory with no window under the same header, so the two tabs read as two different pages answering one question. A retirement is a change that happened on a day: on the timeline it lands beside the work that caused it, with the same colours, authors and filters, and the reader learns it was retired from the row they already scan. The cost is the whole-KB inventory: "every page this KB ever retired" is now the All window read for its pills, and the per-Map archive and journal-harvest counts the tab drew are no longer on a page.

Alternatives rejected. Keeping the tab: two views of one history with different rules, the confusion this change removes. A rail entry for the archive: D820's reason against it still holds, most KBs retire little. Synthetic timeline rows for retirements with no change in the window: the archive and supersede tools always change the concept, so the row exists; a status set by hand is also an edit, and its row says no retirement is recorded.

Consequences. A retired concept's row is matched by its current ID, so a concept moved to an archive Map carries its retirement on the move's row. A narrowed principal that cannot read the retired route sees plain change rows. The archive badge on the rail and search's include_archived (D820) are unchanged.