Wire plan_ready, list_ready, new_suggestions and Send to Google Chat

Connect the features to the notification outbox so real events notify,
each stored by the new notify.EmitTx in the transaction of the change it
is about (Wake after commit):

- plan_ready:{weekStart} (/plan) when a draft job stores the AI's draft;
  a redraft shares the key and a manual swap never emits. The title reads
  "Next week's plan is ready" for the coming week.
- list_ready:{weekStart} (/plan/shopping) when a week's Supply run is
  first created, by generate or after Push to Calendar.
- new_suggestions:{batchId} (/discover) when a scheduled or manual batch
  ends done with cards; replenish batches never notify.
- plan.Service.EmitDayOfReminder(date) emits day_of_reminder:{date} for
  the Feature 20 scheduler.

Add POST /api/v1/shopping/{weekStart}/send-chat: shopping.SendToChat posts
the dinners with needed items and a link through chat.PostSupplyRun,
records sent_to_chat_at, and is idempotent per week unless
{"resend": true}. The Supply run's Send to Google Chat button calls it
("Send again" once sent) and shows failures in an ErrorBanner; the unused
Unavailable placeholder is removed.

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

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

docs/ARCHITECTURE.md

@@ -656,6 +656,25 @@ Runs are recorded in `schedule_runs` and executed through `jobs`.
 - Events: `plan_ready`, `list_ready`, `day_of_reminder`, `new_suggestions`,
   `rotation_review`; each can go to Web Push and/or Google Chat per
   `notification_prefs`.
+- Where each event is emitted, with its idempotency key. Each is stored by
+  `notify.EmitTx` in the transaction of the change it is about, so the
+  change and its notification commit together or not at all:
+  - `plan_ready:{weekStart}` (URL `/plan`) when a draft job stores the
+    AI's draft of a week. Only the first draft of a week notifies: a
+    redraft (Rebuild week) has the same key, and a manual swap never
+    drafts. Its title is "Next week's plan is ready" (or "This week's",
+    or "The plan for the week of Oct 26") and its body the drafted
+    dinners Monday to Sunday.
+  - `list_ready:{weekStart}` (URL `/plan/shopping`) when a week's Supply
+    run is first created, by `POST /shopping/{weekStart}/generate` or
+    after Push to Calendar; remaking it does not notify.
+  - `new_suggestions:{batchId}` (URL `/discover`) when a `scheduled` or
+    `manual` suggestion batch ends done having added Side quests, in the
+    transaction recording it done. A `replenish` batch never notifies.
+  - `day_of_reminder:{date}` (URL `/dinner/{id}`) through
+    `plan.Service.EmitDayOfReminder(date)`, which names the dinner planned
+    on the date and emits nothing for a week with no plan. The scheduler
+    calls it at `reminder_time` (Feature 20).
 - Delivery goes through `notification_outbox`.
 - Web Push uses VAPID (`webpush-go`). Google Chat uses the stored incoming
   webhook.
@@ -880,6 +899,22 @@ Runs are recorded in `schedule_runs` and executed through `jobs`.
   through `shopping.Generate` and answers with the same shape plus
   `skipped: [{date, dinner_id, dinner_name, reason}]`. 404 when the week
   has no plan, 409 `archived` when its list is in the Supply archive.
+- `POST /api/v1/shopping/{weekStart}/send-chat` (CSRF-checked) takes
+  `{}` or `{"resend": true}` and posts the Supply run to Google Chat
+  through `chat.PostSupplyRun`, in the week's thread: "Supply run · " and
+  its title (or week label), each dinner with items still needed and those
+  items, and a card whose "Open" button links to
+  `/plan/shopping?week={weekStart}` under `MEALQUEST_PUBLIC_URL`. It
+  records `sent_to_chat_at` and answers with the Supply run as `GET` gives
+  it. A week already sent is answered as it is, with no second post,
+  unless `resend` is true. No webhook stored is 409 `not_configured`;
+  Google Chat not answering is 502 `chat_unreachable` (retryable) and
+  answering with a status other than 2xx 502 `chat_refused` (retryable
+  only for 429 or 5xx), and neither
+  records `sent_to_chat_at`. 404 when the week has no Supply run, 409
+  `archived` when it is in the Supply archive, 400 `invalid_request` for a
+  bad body. `shopping.SendToChat(weekStart, resend)` is what
+  `shopping_chat_autosend` calls (Feature 20).
 - `PATCH /api/v1/shopping/items/{id}` takes `{needed}` (a required
   boolean; it sets the flag, it does not flip it) and answers `{id,
   needed, needed_count, total_count}` with the list's counts after the