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/recipes/ground.go

@@ -65,7 +65,9 @@ type Grounded struct {
 	// Difficulty is easy, medium or hard.
 	Difficulty string `json:"difficulty"`
 	SourceURL  string `json:"source_url"`
-	SiteName   string `json:"site_name"`
+	// SiteName is the name the page gives its site, "" when it names none
+	// (see Recipe.SiteName).
+	SiteName string `json:"site_name"`
 }
 
 // SearchSource returns the household's current search provider;
@@ -200,8 +202,10 @@ func (g *Grounder) searchRanked(ctx context.Context, dishName, query string) (ra
 // Offer is a ranked candidate offered for the household to ground a dish
 // in, with GroundURL on its URL.
 type Offer struct {
-	URL      string
-	Title    string
+	URL   string
+	Title string
+	// SiteName is the name the page gives its site, "" when it names none
+	// (see Recipe.SiteName).
 	SiteName string
 	// PhotoID is the cached photo of a candidate already stored, "" for
 	// one that is not: a candidate's photo is cached only when it grounds.