Show idea job results' sources safely on every read

GET /jobs/{id} served a succeeded idea job's stored result as it was, so
a result stored before sources were made safe still showed a
token-bearing source_url and a site_name taken from the link's host
(BASE-01-R1). jobs.Kind.FailedResult becomes ShownResult, applied to
every stored result with the job's status: ideas_from_ingredients and
quick_ideas results show no ideas when failed and, otherwise, each
idea's source through dinners.SourceOf, the one rule, so no job old or
new serves an unsafe source. Other kinds' results are untouched.

dinners.SourceOf now parses the link before reading the site name, so a
link that does not parse is an error with or without a stored name, and
an idea job grounded in one fails instead of succeeding (BASE-01-R2).

Task: c15ed4b5-25ae-43c6-8d36-f4a6dd51e5af

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

internal/dinners/export_test.go

@@ -72,8 +72,5 @@ func (s *Service) RunGroundJob(ctx context.Context, p GroundJob) (string, error)
 	return r.GroundingStatus, err
 }
 
-// PageSiteName is pageSiteName.
-var PageSiteName = pageSiteName
-
 // SafeSourceURL is safeSourceURL.
 var SafeSourceURL = safeSourceURL