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>

internal/server/shopping.go

@@ -143,6 +143,70 @@ func patchShoppingItem(logger *slog.Logger, svc *shopping.Service) http.HandlerF
 	}
 }
 
+// supplyArchive is the GET /shopping/archive answer: the Supply archive's
+// periods, newest first, as grouped by by.
+type supplyArchive struct {
+	By      string          `json:"by"`
+	Periods []archivePeriod `json:"periods"`
+}
+
+// archivePeriod is one heading of the Supply archive and its posts,
+// newest first.
+type archivePeriod struct {
+	Key     string        `json:"key"`
+	Heading string        `json:"heading"`
+	Posts   []archivePost `json:"posts"`
+}
+
+// archivePost is one week's Supply run in the Supply archive. label is
+// the week label, which stands in for title while it is null, and
+// onHandCount counts the items marked "have it".
+type archivePost struct {
+	WeekStart   string   `json:"weekStart"`
+	Label       string   `json:"label"`
+	Title       *string  `json:"title"`
+	DinnerCount int      `json:"dinnerCount"`
+	ItemCount   int      `json:"itemCount"`
+	OnHandCount int      `json:"onHandCount"`
+	Dinners     []string `json:"dinners"`
+	Current     bool     `json:"current"`
+}
+
+// getSupplyArchive answers GET /shopping/archive?by=week|month|year with
+// the Supply archive grouped by that period.
+func getSupplyArchive(logger *slog.Logger, svc *shopping.Service) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		by := r.URL.Query().Get("by")
+		periods, err := svc.Archive(r.Context(), by)
+		if errors.Is(err, shopping.ErrInvalidPeriod) {
+			writeError(w, r, logger, http.StatusBadRequest, "invalid_request", shopping.ErrInvalidPeriod.Error())
+			return
+		}
+		if err != nil {
+			writeShoppingError(w, r, logger, "read Supply archive", err)
+			return
+		}
+		out := supplyArchive{By: by, Periods: make([]archivePeriod, len(periods))}
+		for i, p := range periods {
+			posts := make([]archivePost, len(p.Posts))
+			for j, post := range p.Posts {
+				posts[j] = archivePost{
+					WeekStart:   post.WeekStart,
+					Label:       post.Label,
+					Title:       post.Title,
+					DinnerCount: len(post.Dinners),
+					ItemCount:   post.Items,
+					OnHandCount: post.OnHand,
+					Dinners:     post.Dinners,
+					Current:     post.Current,
+				}
+			}
+			out.Periods[i] = archivePeriod{Key: p.Key, Heading: p.Heading, Posts: posts}
+		}
+		writeJSON(w, r, logger, http.StatusOK, out)
+	}
+}
+
 // supplyRunOf is l, the Supply run of the week starting week, as the API
 // shows it.
 func supplyRunOf(week store.LocalDate, l shopping.List) (supplyRun, error) {