Record site-name provenance instead of inferring it from the name's shape

Recipe extraction no longer falls back to the URL's host: a stored
recipes.site_name is now always a name the page gave (publisher or
og:site_name), and null when it named none. dinners.SourceOf is the one
documented rule for every fetched recipe's source: the page's name is
shown as it stands; otherwise the site is named by the link's host only
when the link itself is shown as free of secrets, else null. The recipe
detail, idea results and the recipe-candidate offer endpoint all apply
it; candidates no longer carry an extraction-time hostname fallback, so
their site_name is nullable (frontend updated to match).

Migration 0020 clears host-shaped site names (dotted host names, IP
addresses) stored before the change, in recipes and in legacy idea job
results, so already-stored rows read under the same rule.

Maestro 966066e3-0e25-4b8b-9bb0-0694c47c9106

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

internal/ideas/ideas.go

@@ -486,7 +486,8 @@ func sourceOf(gr recipes.Grounded) (dinners.Source, error) {
 // link sourceURL and site name siteName, as a client may see it (see
 // dinners.SourceOf). A result stored now already holds it, and one stored
 // before sources were made safe holds the grounded recipe's own, with ""
-// for no site name, as sourceOf reads it; a null link, which only a result
+// for no site name, as sourceOf reads it, less any name that could be a
+// host, which migration 0020 cleared; a null link, which only a result
 // stored now holds, is checked as "".
 func shownSource(sourceURL, siteName *string) (dinners.Source, error) {
 	var link string