Add onboarding steps 1 and 2 with the first-run redirect

While household_settings.onboarding_completed_at is null, OnboardingGate
sends every app route to /onboarding, a full screen outside the shell.
The household settings parser now reads onboarding_completed_at from the
existing GET /api/v1/settings/household.

Step 1 welcomes the household and explains Regulars, Side quests and the
Quest log. Step 2 follows mock 1h: progress pills, the add pill with its
grape "+" (Enter also adds), Regulars chips with remove, dashed Common
picks, and "Next: notifications" enabled at 3 Regulars. Adds and removes
go through new dinners API hooks (POST /api/v1/dinners, DELETE
/api/v1/dinners/{id}) optimistically, rolled back if the server refuses.
Step 3 is a placeholder until its task lands.

Maestro task 5a43f813-c940-4f79-a2be-027644ae9e6c.

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

docs/ARCHITECTURE.md

@@ -484,6 +484,15 @@ Runs are recorded in `schedule_runs` and executed through `jobs`.
 `/settings/household`, `/settings/regulars` and `/settings/calendar` come from
 CTXD; the other routes are defined in the UI handoff.
 
+First run: while `household_settings.onboarding_completed_at` (read from
+`GET /api/v1/settings/household`) is null, every route redirects to
+`/onboarding`. Onboarding is a full screen outside the app shell, in three
+steps: the welcome (`/onboarding`), the Regulars (`/onboarding/regulars`,
+mock 1h, adding and archiving through the dinners API optimistically) and
+notifications (`/onboarding/notifications`). Offline on the saved pages the
+settings cannot be read (the service worker never caches `/api/v1/settings`),
+so the saved pages open as they are.
+
 ## Boundaries and gotchas
 
 - **Secrets never reach the client** — API keys, OAuth tokens and the Chat