fix: typed write failures, template rollback, parent and term cleanup

WriteFailed maps to lit_write_failed / lit_partial_write (partial writes are
logged with result partial); old template read before the update; row marker
set before wp_update_post; created terms deleted on rollback; parent must be a
readable non-descendant of a hierarchical type; featured image must be
readable; snapshot keeps empty values; meta comparison after sanitize_meta;
follow-up failures (listener, change log) only add warnings.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Abilities/FollowUp.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Abilities;
+
+use Throwable;
+
+/**
+ * Runs a step after a write has already succeeded (listeners, change log): a failure
+ * there must not turn the saved change into an error. It is logged and reported as warning.
+ */
+final class FollowUp
+{
+    /**
+     * @param list<string> $warnings Receives $warning when the step fails.
+     */
+    public static function run(callable $step, string $context, string $warning, array &$warnings): mixed
+    {
+        try {
+            return $step();
+        } catch (Throwable $e) {
+            $message = sprintf('[wp-lit-mcp] %s failed: %s', $context, $e);
+            error_log($message); // phpcs:ignore WordPress.PHP.DevelopmentFunctions.error_log_error_log
+            $warnings[] = $warning;
+
+            return null;
+        }
+    }
+}