refactor(2meet-data-optimizer): resolve post_type/group/table mappings through the registry

- TMDO_Post_Fields::post_type_for_group() / groups_for_post_type() derive HivePress-style groups from their registry post_type scope (core keeps its own attachment / wc_product / nav_menu_item map); the three copy-pasted switches and the query router's POST_TYPE_GROUP_MAP use them
- Term/comment backfill, shadow verifier and CLI take their groups from the registry (TMDO_Term_Comment_Backfill::registered_groups()); installer drops the hp_* entries already covered by its table patterns; REST listings default post type is filterable (tmdo_rest_default_post_type, default 'post')
- Verify: NoHpMappingsTest guard + mapping/default tests; core unit 640 / integration 449, HP 146/49, WC 10/22 OK
- PR: PR-020e

includes/integrations/class-tmdo-post-fields.php

@@ -43,6 +43,46 @@ if ( ! defined( 'ABSPATH' ) ) {
  */
 final class TMDO_Post_Fields {
 
+	/**
+	 * Post type of each core group that is not scoped to post types in the
+	 * registry (wp_core spans every post type and is absent on purpose).
+	 */
+	private const GROUP_POST_TYPES = array(
+		'attachment'    => 'attachment',
+		'wc_product'    => 'product',
+		'nav_menu_item' => 'nav_menu_item',
+	);
+
+	/**
+	 * Primary post type of a post group: the registry scope for scoped groups
+	 * (e.g. the HivePress AddOn's), the core mapping otherwise.
+	 *
+	 * @param string $group Entity group name.
+	 * @return string|null Null for cross-post-type groups such as wp_core.
+	 */
+	public static function post_type_for_group( string $group ): ?string {
+		$scoped = class_exists( 'TMDO_Entity_Registry' ) ? TMDO_Entity_Registry::get_group_post_types( 'post', $group ) : array();
+		return $scoped[0] ?? ( self::GROUP_POST_TYPES[ $group ] ?? null );
+	}
+
+	/**
+	 * Post groups dedicated to a post type (wp_core excluded).
+	 *
+	 * @param string $post_type Post type slug.
+	 * @return string[]
+	 */
+	public static function groups_for_post_type( string $post_type ): array {
+		$groups = array_keys( self::GROUP_POST_TYPES, $post_type, true );
+		if ( class_exists( 'TMDO_Entity_Registry' ) ) {
+			foreach ( TMDO_Entity_Registry::get_groups_for_type( 'post' ) as $group ) {
+				if ( in_array( $post_type, TMDO_Entity_Registry::get_group_post_types( 'post', $group ), true ) ) {
+					$groups[] = $group;
+				}
+			}
+		}
+		return array_values( array_unique( $groups ) );
+	}
+
 	/**
 	 * Hook into WPDO entity field registration.
 	 *