Freeze ended weeks into the Supply archive and serve the archive API (Feature 17)

shopping.Freeze(weekStart) archives a week's Supply run once its week has
ended in the household's time zone, setting status archived and frozen_at;
it is idempotent, and a week not yet ended (ErrWeekNotEnded) or with no
list (ErrListNotFound) is an explicit error. A list still untitled is
titled first with archive_title and the same conditional write the
title_supply_run job uses; a failed title is logged and the list is
frozen untitled, keeping its week label.

GET /api/v1/shopping/archive?by=week|month|year returns the Supply runs
up to the household's current week, newest first, grouped by the
Monday's ISO week, month or year, each post with its week label, title or
null, dinner, item and on-hand counts, dinner names and current flag. Any
other by is 400 invalid_request. Frozen lists stay readable through
GET /shopping/{weekStart} and reject item PATCHes with 409 archived.

Maestro task 7ac36526-cb51-4dc7-bbad-6ebbee481942.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -490,6 +490,25 @@ automatic** (D-021).
   generation: the list stays untitled (the UI shows the week label), the
   failure is logged as a warning and recorded in `ai_runs`, the job fails
   `title_failed`, and the week's next generation tries again.
+  `shopping.Freeze` titles a list still untitled once more before
+  freezing it (see Supply archive), through the same skill, scope and
+  conditional write.
+
+## Supply archive (Feature 17)
+
+`shopping.Freeze(weekStart)` moves a week's Supply run into the Supply
+archive: `status` becomes `archived` and `frozen_at` is set, after which
+generating the list or changing an item is 409 `archived`. It freezes only
+a week that has ended in the household's time zone (its Monday is before
+the Monday of the household's current week), so a week not yet ended is
+`ErrWeekNotEnded` and a week with no list `ErrListNotFound`; freezing a
+frozen list does nothing. A list still untitled is titled first with
+`archive_title` from the week's plan, as `Generate` titles it; a title
+that cannot be written is logged and the list is frozen untitled, when its
+week label stands in for good. A `title_supply_run` job still in flight
+with the same scope shares that run (`harness.Run`); whichever stores the
+title first wins, and a job storing after the freeze stores nothing. The
+`week_rollover` schedule is to call `Freeze` for last week.
 
 ## Recipe grounding
 
@@ -790,6 +809,20 @@ Runs are recorded in `schedule_runs` and executed through `jobs`.
   needed, needed_count, total_count}` with the list's counts after the
   change. 404 for an unknown item, 409 `archived` when the list is in the
   Supply archive, 400 `invalid_request` for a bad body.
+- `GET /api/v1/shopping/archive?by=week|month|year` returns the Supply
+  archive `{by, periods: [{key, heading, posts: [{weekStart, label,
+  title, dinnerCount, itemCount, onHandCount, dinners, current}]}]}`: the
+  Supply run of every week up to the household's current week, newest
+  first, grouped by the Monday's ISO week (`key` "2026-W41", `heading` the
+  week label), month ("2026-10", "October 2026") or year ("2026"). The
+  Monday is a household-local date, so the week of Monday 28 December
+  is in December. `label` is the week label ("Week 41 · Oct 5 – 11"; the
+  UI sets it in capitals), `title` null while untitled, `dinners` the
+  list's dinners in day order and `dinnerCount` their number,
+  `itemCount` all items, `onHandCount` the items marked "have it", and
+  `current` true for the household's current week. 400 `invalid_request`
+  for any other `by`. A frozen list is read through `GET
+  /api/v1/shopping/{weekStart}` with `status` `archived`.
 
 ## Frontend