feat: Pods fields in Theme Builder bodies checked against the template's post types (E12)

Both forms Divi writes are recognized (ruling Q11): custom_meta_<key> and the
dialog form post_meta_key + select_meta_key. Choice fields get a note about the
stored value, relation fields name IDs (F4). Only templates the user may edit
are checked or named; others are counted (Q21 pattern). Warnings only, also in
the dry run of a live body. DynamicFields extracted from lit/divi-dynamic-sources.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/Integrations/Divi/ThemeBuilder/Template.php

@@ -92,9 +92,18 @@ final class Template
 
     /** @return list<string> Post types of its singular conditions (singular:post_type:<type>:…). */
     public function postTypes(): array
+    {
+        return self::postTypesOf($this->useOn);
+    }
+
+    /**
+     * @param list<string> $useOn
+     * @return list<string>
+     */
+    public static function postTypesOf(array $useOn): array
     {
         $types = [];
-        foreach ($this->useOn as $condition) {
+        foreach ($useOn as $condition) {
             $parts = explode(':', $condition);
             if (($parts[0] ?? '') === 'singular' && ($parts[1] ?? '') === 'post_type' && ($parts[2] ?? '') !== '') {
                 $types[] = $parts[2];