Fix Feature 12 review findings F2–F8 on Regular grounding and onboarding

Grounding (F2–F5):
- Each ground_dinner job carries the dinner's new grounding_revision
  (migration 0010). Renaming a pending Regular raises the revision, and a
  job only grounds and writes a dinner still at its revision, so a queued
  original job no longer grounds the new name or decides the outcome.
- Background grounding keeps a method, minutes or difficulty a member saved
  while the Regular was pending, and fills only those left empty.
- Grounding by hand clears the pasted recipe_url, and link deduplication
  uses the source_url of the attached recipe, else the pending link.
- Archived dinners are not grounded: the job checks before any search,
  fetch or model call, and its final update requires an unarchived row.

Onboarding (F6, F7):
- Step 3 shows "Add Regulars" back to step 2 when the server refuses to
  finish with fewer than three Regulars.
- Common picks are hidden by a copy of harness Normalize/Similar, checked
  against the same shared cases as the Go code.

Docs (F8): ARCHITECTURE.md covers the three-Regular minimum, step-3
recovery, the grounding revision and the dedupe rules.

F1 was fixed in 1304487; its test now also asserts the old link is never
grounded and recipe_url stays cleared.

Maestro task 5037ff86-181d-448e-927b-c2fd2258a25d.

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

web/src/settings/api.ts

@@ -441,6 +441,18 @@ export function householdSettingsProblems(error: Error): HouseholdSettingsProble
   return problems
 }
 
+// needsMoreRegulars reports whether error is the server refusing to finish
+// onboarding because the household has fewer than three Regulars
+// (internal/household MinRegulars) — the only refusal of
+// {"onboarding_completed": true}.
+export function needsMoreRegulars(error: Error): boolean {
+  return (
+    error instanceof ApiError &&
+    error.code === 'invalid_settings' &&
+    error.message.startsWith(`${invalidHouseholdPrefix}onboarding_completed: `)
+  )
+}
+
 // aiStatus is the AI assistant row's status line: the provider and the
 // model's display name, or that no model is chosen yet (the seed).
 export function aiStatus(settings: Pick<AISettings, 'provider' | 'model'>): string {