Make new_suggestions and Send to Google Chat recoverable

MQ-167-01: a scheduled or manual batch now emits new_suggestions:{batchId}
in the transaction that first stores its Side quests, so the cards and
their notification commit together. A later round that fails, or a
failure recording the batch's end, no longer loses the event; a later
round's emit is a no-op by key; a notification that cannot be stored
fails that store, leaving no unannounced cards. Replenish batches still
never notify. finishBatch goes back to recording status only.

MQ-167-02: migration 0017 adds shopping_lists.chat_send_unconfirmed_at.
SendToChat records the send as begun before posting, clears it with
sent_to_chat_at once Google Chat accepts, and clears it alone when Chat
refuses. A post Chat does not answer, or one it accepts that cannot be
recorded, is ErrSendUnconfirmed (502 chat_unconfirmed, not retryable)
and leaves the marker, as does a crash mid-send; a repeat without resend
never reposts, and resend posts again. The Supply run screen re-reads
the list after a failed send, shows an unconfirmed send, offers no Retry
for it, and sends again only with resend.

Task: f0cd9d50-9c11-41be-a945-7bae9f5f28a4

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

internal/shopping/shopping.go

@@ -82,6 +82,12 @@ var ErrItemNotFound = errors.New("no Supply run has that item")
 // the household's time zone.
 var ErrWeekNotEnded = errors.New("the week has not ended")
 
+// ErrSendUnconfirmed is a send to Google Chat whose outcome is not known:
+// Google Chat did not answer, or accepted the post but recording it failed.
+// The post may have been made, so the Supply run keeps the send as
+// unconfirmed and is posted again only with resend.
+var ErrSendUnconfirmed = errors.New("the shopping list may have reached Google Chat, but that could not be confirmed; check the space before sending again")
+
 // ErrInvalidPeriod is an Archive grouping other than ByWeek, ByMonth and
 // ByYear.
 var ErrInvalidPeriod = errors.New("by must be week, month or year")
@@ -158,7 +164,11 @@ type List struct {
 	// SentToChatAt is when the list was sent to Google Chat; nil until it
 	// is.
 	SentToChatAt *string `json:"sent_to_chat_at"`
-	Groups       []Group `json:"groups"`
+	// ChatSendUnconfirmedAt is when a send to Google Chat whose outcome is
+	// not known began: one under way, or one that may or may not have been
+	// posted. nil when there is none.
+	ChatSendUnconfirmedAt *string `json:"chat_send_unconfirmed_at"`
+	Groups                []Group `json:"groups"`
 }
 
 // Counts are how many items of a Supply run are still needed and how many
@@ -563,13 +573,14 @@ func frozen(list db.ShoppingList) bool {
 // listOf is list with groups.
 func listOf(list db.ShoppingList, groups []Group) List {
 	return List{
-		ID:           list.ID,
-		WeekStart:    list.WeekStart,
-		PlanID:       list.PlanID,
-		Title:        nullString(list.Title),
-		Status:       list.Status,
-		SentToChatAt: nullString(list.SentToChatAt),
-		Groups:       groups,
+		ID:                    list.ID,
+		WeekStart:             list.WeekStart,
+		PlanID:                list.PlanID,
+		Title:                 nullString(list.Title),
+		Status:                list.Status,
+		SentToChatAt:          nullString(list.SentToChatAt),
+		ChatSendUnconfirmedAt: nullString(list.ChatSendUnconfirmedAt),
+		Groups:                groups,
 	}
 }