Register the weekly suggestions schedule (Feature 20)

suggest.Service.WeeklySchedule fires at the household suggestions_dow and
suggestions_time (default Sunday 08:00) with period key
suggestions_weekly:YYYY-Www and starts a scheduled batch through the same
service and job as the API, via the new StartScheduledBatch(week).
StartBatch now refuses the scheduled trigger.

new_suggestions is still emitted only where Feature 19 put it, in the
transaction that stores a batch's Side quests. A scheduled batch is now
keyed new_suggestions:YYYY-Www by the week carried in its job, so a
batch caught up late keeps its own week's key; a manual batch stays keyed
by its id. The title counts the new Side quests. A batch whose AI call
fails stores nothing and sends nothing; the failure is in ai_runs.

Fake-clock tests in internal/scheduler cover one batch and one
notification per week, settings-driven fire time, AI failure, restart,
late catch-up and a batch already under way.

Maestro task 459aab71-5c3d-4853-9855-236a3602b1e0

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

internal/chat/messages_test.go

@@ -110,9 +110,19 @@ func TestMessages(t *testing.T) {
 			key:   "new_suggestions:01J9BATCH",
 			url:   "/discover",
 			week:  "2026-10-12",
-			title: "New Side quests are in",
+			title: "5 new Side quests are in",
 			body:  "Lemon orzo, Bibimbap, Shakshuka + 2 more",
-			chatT: "New Side quests are in: Lemon orzo, Bibimbap, Shakshuka + 2 more. Open Discover →",
+			chatT: "5 new Side quests are in: Lemon orzo, Bibimbap, Shakshuka + 2 more. Open Discover →",
+		},
+		{
+			name:  "new suggestions of a scheduled week",
+			ev:    NewSuggestions("2026-W42", week, []string{"Pho"}),
+			key:   "new_suggestions:2026-W42",
+			url:   "/discover",
+			week:  "2026-10-12",
+			title: "1 new Side quest is in",
+			body:  "Pho",
+			chatT: "1 new Side quest is in: Pho. Open Discover →",
 		},
 		{
 			name:  "rotation review",