Hide the recipe link, pick the creating suggestion, refuse duplicate positions

Dinner detail review fixes for GET /api/v1/dinners/{id}:

- source is now {site_name} with no url. A stored source_url may be a
  pasted or offered link carrying a personal token, and nothing can show
  a stored link is free of one; the candidate flow keeps every page URL
  on the server for the same reason, so the detail does too.
- why_picked comes from GetDinnerSuggestionReasons, which reads only
  pending or accepted suggestions: a suggestion is only ever created with
  a new dinner and declining one archives that dinner, so a declined row
  never created a live dinner. More than one candidate row is an error
  rather than a guess. sqlc regenerated.
- Two recipe ingredients or steps at one position leave recipe order
  unknown, so the read fails rather than ordering them by id.

Maestro task 099e9952-7f98-4700-8369-241c589a1e9d.

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

docs/ARCHITECTURE.md

@@ -213,10 +213,15 @@ automatic** (D-021).
   raw_text}]` and `steps` the step texts, both in recipe position order and
   empty (`[]`) with no recipe, as for a dinner whose grounding is
   `pending` or `failed`; a recipe entered by hand has only `raw_text`.
-  `source` is `{url, site_name}` of the page the recipe was fetched from,
-  null for a manual recipe or none; `why_picked` is the reason of the
-  suggestion that created the dinner (its earliest), null for one no
-  suggestion created. An unknown or archived dinner is 404.
+  Two items at one position leave recipe order unknown, so such a recipe
+  is 500 rather than shown out of order. `source` is `{site_name}` of the
+  page the recipe was fetched from (`site_name` null when the page names
+  none), null for a manual recipe or none; it has no `url`, as the page's
+  link may carry a personal token. `why_picked` is the reason of the
+  suggestion that created the dinner — its pending or accepted one, as
+  declining a suggestion archives its dinner — null for one no suggestion
+  created; a dinner with more than one such suggestion is 500, as nothing
+  records which created it. An unknown or archived dinner is 404.
 - Dinner grounding. `POST /api/v1/dinners` also enqueues a `ground_dinner`
   job and answers with its `grounding_job_id` without waiting for it
   (`GET /api/v1/jobs/{id}` reports it); if the job cannot be enqueued it