fix(2meet-data-optimizer): add declared flat-table indexes from WP-CLI or WP-Cron only, one process at a time

- ensure_group_indexes() runs the ALTER only under WP-CLI or WP-Cron (filter
  tmdo_schema_ddl_allowed); web requests, including /wp-admin/ before
  auth_redirect() and admin-post.php, schedule tmdo_ensure_group_indexes instead
- MySQL GET_LOCK keeps it to one process (add_option() is INSERT ... ON
  DUPLICATE KEY UPDATE and cannot serve as a lock); released by MySQL if the
  process dies
- the applied signature is recorded only when every ALTER succeeds; failures
  log schema.index_failed and stay in pending_indexes(), which doctor reports
- new tables get their declared cidx_ indexes in CREATE TABLE
- test stub wpdb::query()/insert() return false on SQL errors like wpdb
- Verify: GroupCompositeIndexTest 7/7, unit 698, integration 576, phpcs, stan
- PR: PR-090a

includes/class-tmdo-installer.php

@@ -789,6 +789,7 @@ class TMDO_Installer {
 		wp_clear_scheduled_hook( 'wpdo_post_shadow_verify' );
 		wp_clear_scheduled_hook( 'wpdo_term_comment_shadow_verify' );
 		wp_clear_scheduled_hook( 'tmdo_drift_resync' );
+		wp_clear_scheduled_hook( 'tmdo_ensure_group_indexes' );
 		wp_clear_scheduled_hook( 'wpdo_post_stress_test_batch' );
 		wp_clear_scheduled_hook( 'wpdo_user_stress_test_batch' );
 		wp_clear_scheduled_hook( 'wpdo_term_stress_test_batch' );
@@ -993,6 +994,7 @@ class TMDO_Installer {
 			'wpdo_post_shadow_verify',
 			'wpdo_term_comment_shadow_verify',
 			'tmdo_drift_resync',
+			'tmdo_ensure_group_indexes',
 			'wpdo_post_stress_test_batch',
 			'wpdo_user_stress_test_batch',
 			'wpdo_term_stress_test_batch',