Add day-of and crock-pot start-by reminders (Feature 20)

Register plan.Service.ReminderSchedules as the day_of_reminder schedule:
daily at the household reminder_time (period YYYY-MM-DD) it emits
day_of_reminder:YYYY-MM-DD, "Tonight: {dinner} · Recipe →" linking
/dinner/{id}; for a crock-pot dinner whose start_by is earlier than
reminder_time it also fires 15 minutes before start_by (period
start:YYYY-MM-DD) and emits day_of_reminder:start:YYYY-MM-DD, "Start the
crock pot by {time}". A date whose week has no plan emits nothing.

The scheduler gains DailyAt rules, whose fire time per date is looked up
from data on every pass (a failed lookup is retried every ClaimRetry),
and a Schedule Key that prefixes period keys so two schedules of one
name claim different periods.

Maestro task 30963b62-2803-4879-82ff-c351cc6628cf.

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

docs/ARCHITECTURE.md

@@ -782,7 +782,7 @@ purge are fixed and not configurable.
 | `suggestions_weekly` | Sunday 08:00 | New batch of Side quests (`suggest.Service.WeeklySchedule`). |
 | `plan_draft` | Friday 09:00 | AI drafts next week's plan (`plan.Service.DraftSchedule`). |
 | `shopping_chat_autosend` | Saturday 08:00 | Sends the Supply run to Google Chat. |
-| `day_of_reminder` | Daily 16:30 | Tonight's dinner reminder. |
+| `day_of_reminder` | Daily 16:30, and 15 minutes before a crock-pot start_by earlier than that | Tonight's dinner reminder and the crock-pot start reminder (`plan.Service.ReminderSchedules`). |
 | `rotation_check` | Daily 09:00 | Asks "Keep it in rotation?" for tried dinners. |
 | `week_rollover` | Monday 00:05 (fixed) | Freezes last week's Supply run into the Supply archive. |
 | `ai_runs` purge | Daily (fixed) | Calls `harness.Purge` to delete `ai_runs` rows past 30-day retention (Feature 20). |
@@ -790,7 +790,7 @@ purge are fixed and not configurable.
 Runs are recorded in `schedule_runs` and executed through `jobs`.
 
 `internal/scheduler` runs them. A schedule registers a name, a rule read
-from the settings (`scheduler.Daily`, `Weekly` or `WeeklyForNextWeek`) and a
+from the settings (`scheduler.Daily`, `Weekly` or `WeeklyForNextWeek`, or `DailyAt` for a time read from data) and a
 run function; settings changes reach it through `SettingsService.Subscribe`
 and move the next fire time without a restart. Each fire time has a period
 key (`Rule.PeriodKey`): the local date for a daily rule, the ISO week of the
@@ -822,6 +822,19 @@ draft emits `plan_ready:{weekStart}` from the job and a failed one (e.g.
 `ai_failed`, recorded in `ai_runs`) emits nothing. When the week already
 has a plan, in any status, it enqueues nothing; when a draft of the week
 is already queued or running it joins it. Either way it logs it.
+`plan.Service.ReminderSchedules()` is `day_of_reminder`, two schedules
+of one name. The first is `Daily(reminder_time)`, period `YYYY-MM-DD`,
+and calls `EmitDayOfReminder(period.Date)`. The second has `Key` `start`,
+so its periods are `start:YYYY-MM-DD`, and a `scheduler.DailyAt` rule:
+for each date it reads the plan and fires 15 minutes
+(`plan.StartReminderLead`) before the day's `start_by` (the same
+computation the plan API shows) when the dinner is a crock-pot dinner
+whose `start_by` is earlier than that day's `reminder_time`; its run
+calls `EmitStartReminder(period.Date)`, which checks the same again. A
+date whose week has no plan emits neither and logs it. A `DailyAt` fire
+time is looked up from the data on every pass, so a plan change moves it
+within an hour (`maxWait`); a lookup that fails is logged and repeated
+every `ClaimRetry`.
 Fake-clock tests of a schedule live in `internal/scheduler`, where
 `SetClock` is visible to tests.
 
@@ -857,9 +870,15 @@ Fake-clock tests of a schedule live in `internal/scheduler`, where
     notifies. This is the only place `new_suggestions` is emitted; the
     `suggestions_weekly` schedule does not emit it itself.
   - `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).
+    `plan.Service.EmitDayOfReminder(date)`, "Tonight: {dinner} · Recipe →",
+    naming the dinner planned on the date; it emits nothing for a week
+    with no plan. The `day_of_reminder` schedule calls it at
+    `reminder_time`.
+  - `day_of_reminder:start:{date}` (URL `/dinner/{id}`) through
+    `plan.Service.EmitStartReminder(date)`, "Start the crock pot by
+    {time}" with the dinner's name, only for a crock-pot dinner whose
+    `start_by` is earlier than `reminder_time`. The `day_of_reminder`
+    schedule calls it 15 minutes before `start_by`.
 - Delivery goes through `notification_outbox`.
 - Web Push uses VAPID (`webpush-go`). Google Chat uses the stored incoming
   webhook.