Withhold unsafe recipe sources from idea job results

Cook from what I have and Quick dinners ideas returned the grounded
recipe's raw source_url and site_name, so a link carrying a token in its
query or userinfo, or a stored name taken from its host, reached the
client in the job response (BASE-01).

dinners.SourceOf is now the one way a fetched recipe's source reaches a
client: the dinner detail and both idea result builders use it. An
idea's source_url and site_name are null when they could leak a secret,
and a source that does not parse fails the job instead of being shown.

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

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

internal/dinners/detail.go

@@ -147,11 +147,11 @@ func readRecipe(ctx context.Context, q *db.Queries, recipeID string, d *Detail)
 		return fmt.Errorf("recipe %s: %w", recipeID, err)
 	}
 	if !IsManualRecipe(rec.SourceUrl) {
-		site, err := pageSiteName(rec.SiteName, rec.SourceUrl)
+		src, err := SourceOf(rec.SiteName, rec.SourceUrl)
 		if err != nil {
 			return err
 		}
-		d.Source = &Source{SiteName: site, URL: safeSourceURL(rec.SourceUrl)}
+		d.Source = &src
 	}
 	ings, err := q.ListRecipeIngredients(ctx, recipeID)
 	if err != nil {
@@ -182,6 +182,19 @@ func readRecipe(ctx context.Context, q *db.Queries, recipeID string, d *Detail)
 	return nil
 }
 
+// SourceOf is the Source of a recipe fetched from sourceURL whose stored
+// site name is siteName: the name only when the page gave it (see
+// pageSiteName) and the link only when it is free of secrets (see
+// safeSourceURL). It is the one way a fetched recipe's source reaches a
+// client.
+func SourceOf(siteName sql.NullString, sourceURL string) (Source, error) {
+	site, err := pageSiteName(siteName, sourceURL)
+	if err != nil {
+		return Source{}, err
+	}
+	return Source{SiteName: site, URL: safeSourceURL(sourceURL)}, nil
+}
+
 // pageSiteName is the stored site name of a recipe fetched from sourceURL
 // when it is one the page gave, else nil. A page that names no site is
 // stored under recipes.HostSiteName of the URL it was served from: the