fix: IndexNow hears of deleted and edited records

RecordDeleted marks the listed rows it excludes and RecordSaved the rows
whose lastmod it moves (indexnow_pending_at); the next rebuild sends
them to IndexNow as removed or changed and clears the marks. RecordSaved
checks for a nil event before reading it. TestIndexNow now deletes and
edits through the record events, as the admin does.

models/url.go

@@ -51,7 +51,10 @@ type Ref struct {
 // its sitemap-images file (nil while it has none). Kind is the content
 // type's kind (pact.ContentKindArticle and the others), PublishedAt the
 // record's first publication and ParentRefs its parents, for the News
-// sitemap and the HTML sitemap.
+// sitemap and the HTML sitemap. IndexNowPendingAt is set by the record
+// listeners on a row the next rebuild sends to IndexNow (a deleted
+// record's listed row, an edited record's row whose lastmod moved) and
+// cleared by that rebuild.
 type URL struct {
 	ID             uint64                       `gorm:"column:id;primaryKey"`
 	Grp            string                       `gorm:"column:grp"`
@@ -71,6 +74,8 @@ type URL struct {
 	ParentRefs     lagoon.Jsonable[[]Ref]       `gorm:"column:parent_refs"`
 	ExcludedReason string                       `gorm:"column:excluded_reason"`
 	UpdatedAt      time.Time                    `gorm:"column:updated_at"`
+	// IndexNowPendingAt (P33-62).
+	IndexNowPendingAt *time.Time `gorm:"column:indexnow_pending_at"`
 }
 
 func (URL) TableName() string { return "golem15_sitemap_urls" }