Add CObjectTemplate marker interface for cache templates

ITEM, DEED and RUNE templates share one id space (JSON-Refactor-Plan D1).
Empty for now; the shared getters come with Task 1.1.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/engine/parsers/objects/DeedTemplate.java

@@ -27,7 +27,7 @@ import java.util.LinkedHashMap;
 //
 // Read only once loaded.
 
-public class DeedTemplate {
+public class DeedTemplate implements CObjectTemplate {
 
     public static HashMap<Integer, DeedTemplate> _deeds = new HashMap<>();