feat: graph validation and custom JSON-LD

- seo_schema (seoschema, E8) with the C17 server rules: invalid JSON with
  line and column, non-objects, 16 KB, depth 8, a literal <script and a
  type outside the kind's list refused; the value re-serialised
- a custom node with a generated @id merges into it (schema.merged save
  notice), other nodes are appended to the graph
- seo_primary_parent (seoparent) for article types; both values stored
  in the entry data on every locale row
- the seo_graph widget action (E9 data), P1 primary_gone and the P2
  schema type and breadcrumb trail rows
- GET /_seo/api/v1/graph and MCP seo_get_graph; seo_set_url_seo and
  apply_batch accept primary_parent and schema

The graph tool lands with the validation: the operations parity test
binds the seo_graph widget action to its tool.

classes/entries.go

@@ -22,6 +22,30 @@ var EntryColumns = []string{
 // every locale row (Q-5): the social image.
 const SharedColumn = "og_image"
 
+// DataColumns are the SEO tab values stored in an entry's data (P33-23):
+// the primary parent and the structured data value. Like the social image
+// they are one per record, written on every locale row.
+var DataColumns = []string{DataPrimaryParent, DataSchema}
+
+// sharedColumns are every value shared by the locale rows of a record.
+var sharedColumns = append([]string{SharedColumn}, DataColumns...)
+
+// SharedData returns a record's shared data value: the first non-empty
+// value in locale order.
+func SharedData(entries map[string]models.Entry, key string) string {
+	locales := make([]string, 0, len(entries))
+	for locale := range entries {
+		locales = append(locales, locale)
+	}
+	sort.Strings(locales)
+	for _, locale := range locales {
+		if v := entryData(entries[locale], key); v != "" {
+			return v
+		}
+	}
+	return ""
+}
+
 // SharedValue returns a record's shared social image: the first non-empty
 // value in locale order.
 func SharedValue(entries map[string]models.Entry) string {
@@ -61,6 +85,8 @@ func entryValue(e models.Entry, column string) string {
 		return e.OGDescription
 	case "og_image":
 		return e.OGImage
+	case DataPrimaryParent, DataSchema:
+		return entryData(e, column)
 	}
 	return ""
 }
@@ -85,6 +111,17 @@ func setEntryValue(e *models.Entry, column, value string) {
 		e.OGDescription = value
 	case "og_image":
 		e.OGImage = value
+	case DataPrimaryParent, DataSchema:
+		data := models.JSONMap{}
+		for k, v := range e.Data {
+			data[k] = v
+		}
+		if value == "" {
+			delete(data, column)
+		} else {
+			data[column] = value
+		}
+		e.Data = data
 	}
 }
 
@@ -152,7 +189,11 @@ func (s *Service) SaveRecord(ctx context.Context, db *gorm.DB, in RecordWrite) (
 	}
 	described := s.recordLocales(ctx, in.Type.Key, in.ID)
 	values := in.Values
-	if shared, ok := values[SharedColumn]; ok {
+	for _, column := range sharedColumns {
+		shared, ok := values[column]
+		if !ok {
+			continue
+		}
 		// One value for every locale of the record (Q-5).
 		v := ""
 		for _, text := range shared {
@@ -166,10 +207,10 @@ func (s *Service) SaveRecord(ctx context.Context, db *gorm.DB, in RecordWrite) (
 			all[locale] = v
 		}
 		copied := RecordValues{}
-		for column, perLocale := range values {
-			copied[column] = perLocale
+		for c, perLocale := range values {
+			copied[c] = perLocale
 		}
-		copied[SharedColumn] = all
+		copied[column] = all
 		values = copied
 	}
 	touched := map[string]models.Entry{}